DIY Promaster Camper Conversion Guide – Part I

ram-promaster-campervan-conversion-interior-built

This year my husband Joel and I decided to do something crazy and head out on a 2-year long road trip through Central and South America. We were super excited for this trip but we had one problem- no transportation.

We recently sold our converted Honda Element camper suv in order to get something bigger for the long trip.

With a tiny budget and not a whole lot of money, we couldn’t afford to spend our entire savings on buying a decked out $100k+ camper van so instead we decided to put our own brains and hands to work and do our own awesome DIY custom camper van conversion.

awesome DIY homemade promaster campervan conversion

We found the perfect, slightly used Ram Promaster van for $20K and over the next 3 months converted the blank cargo van into a fully livable custom built camper for just under $3k in conversion cost.

Our guide below covers exactly how we did our DIY camper conversion for anyone inspired to join the van life movement themselves on a low-cost budget.

amazing DIY custom promaster campervan conversion

To make this Promaster camper van conversion guide easier to follow, we divided our how to guide into two parts. Part I will cover the conversion planning, layout design ideas and all of the prep work we did that’s not necessarily visible but make everything work. Part II will cover the construction of the finished product and any extras we added to make our van life travel on the road more comfortable.

Promaster Campervan Conversion Guide-Part I

1. Layout & Must Haves
2. Installing Windows & Fan
3. Wiring & Electrical
4. Insulation

1. Layout & Must Haves

When we bought the Ram Promaster van it was an empty room on wheels so the first task of our van conversion process was to come up with some campervan conversion ideas.

van to campervan conversion ideas

During our research, we couldn’t find any low-cost Ram Promaster conversion kits so we had to create our own customized layout and plan from scratch. After all, one of our main goals was to keep our van conversion cost as low as possible and we also liked the idea to have the freedom to modify anything in our van to make it look amazing and unique instead of using a generic kit.

Some of our DIY van conversion must have requirements were:

  • Permanent bed with storage under the bed
  • Fridge
  • A kitchen area with permanent cooking stove
  • Sink with running water
  • Sliding windows for light and air circulation
  • Fan in the roof
  • Space for our cat
  • Swivel seat for the passenger

promaster campervan conversion layout plan

We had a basic idea that we wanted the kitchen to be in the front against the left wall and the bed in the back. Everything else we had to figure out as we built the van.

2. Installing Windows & Fan

Before we started with any interior work, the first task was to cut out holes in the van for the windows and fan. This was actually one of the scariest tasks to do because if something went wrong in this step, the van would be ruined. Sounds fun, right?

DIY promaster campervan conversion window cutting

To install windows and a fan, you’ll need:

  • As many windows as you’d like to add
  • An RV roof fan
  • Black butyl tape
  • A reciprocating saw with a metal blade
  • Paint to touch up the cut edges

We wanted to install two sliding windows in our campervan to allow air in, add better vision and circulate air for cooking. We wanted to add one window on each side, one on the sliding door and one behind the driver’s seat.

used campervan conversion installing windows

The sliding windows we chose came in medium size with screens to protect against bugs at night. We bought the windows from a local RV surplus store instead of going with the windows that are made specifically for Ram Promasters by CR Lawrence. The RV surplus store windows cost only $30 each and came with screens and trim rings compared to the others that cost around $500 a piece.

DIY promaster camper van conversion cutting roof for fan

Besides cutting two holes for the windows, we also cut a hole in the roof for the fan. We decided to install the fan towards the back of the van above the bed to get better circulation as the air comes through the sliding windows in the middle of the van and out the fan in the back.

DIY promaster campervan conversion installing ceiling fan

We used a MaxxAir RV roof fan with multiple speeds and a temperature sensor that can be set to automatically turn on the fan if the van gets too hot.

We used a reciprocating saw to cut the hole for the fan and a hole puncher powered by compressed air to cut the window holes. The hole puncher left a smoother edge and less fine cuttings which tend to dig themselves into the paint and can cause tiny rust spots to appear.

how to install RV windows in promaster van conversion

When installing the windows and fan, we touched up every cut edge with white paint so it wouldn’t rust and used this black butyl tape to seal everything off from water leaks.

Cutting all three holes right after purchasing the van was intimidating at first, but after making the first cut it didn’t feel so scary after all.

3. Wiring & Electrical

We are not electrical engineers so at first wiring seemed pretty intimidating to take on, but it turned out to be a lot simpler than we thought.

promaster campervan conversion guide wiring

To do the wiring part of the conversion you will need:

  • 1 or 2 deep cycle batteries
  • Battery isolator relay
  • Fuse block
  • 2 different colored rolls of 16 GA cable
  • 2 different colored rolls of 12 GA cable
  • 1 roll of 6 GA cable
  • Pack of 12V switches from Amazon
  • LED lights
  • LED String lights (optional for decoration)
  • Wire cutters/crimpers
  • Wire connections

(optional)

  • 1-2 solar panels
  • solar charge controller
  • 10 gauge cable
  • inverter

The first step is to draw a diagram of your electrical system.

promaster campervan conversion simple electrical wiring diagram

Our electrical system would include two deep-cycle Group 31 batteries (our “house” batteries) being charged by the car’s alternator while driving and a single solar panel on the roof. This system will easily power our LED lights, fridge, and water pump and have extra juice to charge our camera gear and computers.

Instead of installing an expensive pure sine wave inverter to power up our electronics, we just bought car chargers for the few things that aren’t already powered from a USB drive.

how to wire promaster van for vanlife travel

We used a battery isolator relay to charge the two house batteries from the car’s alternator while driving but disconnect them when the car is off, preventing us from discharging the main car battery and getting stranded in the middle of nowhere. This system worked great on our Honda Element conversion as long as we turned on the car for at least 15 minutes a day.

how to install house batteries promaster campervan conversion

The two house batteries were placed in the rear of the van between the rear wheel wells to distribute the weight to the back a bit. This location worked out great because we could easily place the fuse blocks and solar charge controller right above it and have easy access to them in case something goes wrong.

promaster campervan conversion tiny budget

For the batteries, we used two deep-cycle group 31 batteries from Pepboys that seem to always be on sale for around $50 each. They are regular lead-acid batteries that could potentially release harmful gasses so they need to be in a sealed compartment. We created the sealed compartment using 3/4” plywood and high-density foam weatherstrip between the lid and the box, then used a ¾” hose vented to the outside right below the taillight.

ram promaster van conversion lights

We used LED lighting all throughout because they are really efficient and don’t get hot like regular lights do. For when we need bright lights we installed five really efficient and bright LED puck lights on the ceiling and for when we want mood lighting we hung dimmable LED string lights all around the van. We used the 6th puck light under the bed in the rear storage compartment.

how to install solar panel promaster campervan conversion

We also decided to add a solar panel on the roof of the van to help keep the batteries maintained on sunny days when we don’t do a lot of driving. Adding a solar panel is extremely easy and just needs two more components: a 12V solar panel and a $20 solar charge controller. We found a used 145-watt solar panel for practically nothing on Craigslist and installed it on the roof, then drilled a small hole on the roof to run the two wires in and sealed it with a self-leveling sealant made especially for RV and van roofs.

4. Insulation

Before building up the interior of the Promaster van we wanted to install insulation to keep the van cooler in hot temperatures and warmer in cold temperatures.

Out of all the insulation types, we decided R-max polyiso rigid foam insulation board from Home Depot would be the best fit for our van conversion because:

  • It’s mold proof so it doesn’t need a vapor seal
  • it’s non-toxic so it doesn’t need to be completely sealed off from the living space
  • it’s rigid so it won’t shift or settle down with vibration
  • it has the highest insulation value per inch of thickness so we can maximize interior space

The only downside to rigid foam insulation is that it takes a while to cut and fix into every panel, but considering we don’t need to seal it off completely, it still takes less time than insulating with soft fiber insulation.

van conversion process ceiling insulation for promaster

What you’ll need to do the insulation:

  • three 1” R-Max polyiso rigid foam boards
  • five ½” R-Max polyiso rigid foam boards
  • 1 roll of aluminum duct tape
  • 1 tube of foamboard adhesive
  • a box cutter

We bought 1” and ½” insulation panels to use. We installed a double layer of 1” insulation on the bottom wall side panels and 1” insulation on the top back wall side panels to maximize space for sleeping at night.

We then used foamboard adhesive to stick the insulation onto the walls and flexible duct tape to seal around the edges.

promaster van conversion process windows

For the space around the side windows, we cut out 1/2” insulation and covered it in white cloth. This gave the windows a really nice finished look that was much easier to make than paneling.

On the ceiling, we installed 1/2“ insulation during our conversion to maximize standing room for cooking and hanging out. Since we put a large solar panel and roof rack on top of the van that would act as a constant shade we didn’t need thicker insulation in the ceiling anyway.

how to install ceiling insulation promaster campervan conversion

We painted all the ceiling insulation panels white because we were planning to install roof slats and we didn’t want any colors to peek through the slats.

During the conversion’s insulation step we only sealed off the large panels and didn’t bother with the smaller crevices. On our previous SUV camper conversion  we used a foam gap sealant to seal off all the small areas and ended up making a huge mess from the dripping sealant that was impossible to clean off. We found that sealing off every small area doesn’t add too much more insulation value if the big areas are sealed off properly already so we decided it was best to avoid all the hassle and mess.

ram promaster awesome van to campervan conversion

With the windows, fan, electrical, and insulation in place, we were ready to seal it all up and start working on building up the van interior and giving our Promaster conversion a finished customized look.

In Part 2 of our DIY homemade van conversion process, we will go over how we did the camper van’s interior build and all the extras that we added on to our conversion to make our van life more comfortable.

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Related Article:

50 Van Life Tips For Living On The Road

How To Convert Your SUV Into A Camper

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Elijah

Where did you get your windows for 30$??? I’ve looked everywhere and can’t seem to find them.

Adrian D Moon

Super clean and simple, great stuff here! Thanks a bunch for sharing all of this. One question… how did you mount the 80/20 system up top? I’m doin this for sure. Did you drill into the roof or find a way to use the factory mounts?

THANKS!! Awesome job.

Thanks Adrian! We used the factory mounting studs on the roof and created some diy mounts. For this, we used aluminum square tubing like these cut into 6 inch long pieces. The flange part pointed up and the roof rack was screwed onto the flange. On the bottom of the square tubing, we made oval holes where they drop over the factory mounting studs. Then, we used smaller square tubing like these that fit inside the larger tubing, cut them into 3 inch pieces, and cut a slit along the middle where it allows the mounting stud to slide through.… Read more »

Matt

I do have a couple of questions; one, what isolator did you use and here did you locate it? Also, it looks like you didn’t put in any roof insulation? I’m assuming this was to save the standing height? And, would you put insulation in if you were to redo this build?
Thanks, Matt

We used this isolator which has worked out great. We put it under the van, right behind the van’s battery tray. We then used 6 gauge wiring to connect it all. Just make sure to add inline fuses to both sides of the cable in case there’s an issue anywhere along the wiring.

Matt

Never mind the insulation questions?! I was reading too quickly on this part of the build page. SO, would you go with thicker insulation for energy sake if you were doing this again?

The half inch of insulation on the ceiling has been good for us, but having the roof rack with wooden slats and a solar panel that partially block the sun makes a huge difference. If I didn’t mind losing some height and I had to choose either adding more insulation to the ceiling or the floor, I would choose the floor since you can feel the heat/cold when you walk on it. But overall our insulation works for us and wouldn’t change it. The only thing I would do differently about the insulation on our van would be the windows.… Read more »

Matthew Landon

Again, thank you for the information, Joel! Really impressed with your rack set up and the diy mounting plates, that seems very doable and easy enough to replicate. Thank you for the advice on the isolator and insulation. I used that similar style of isolator on my first couple of campers, but it seems that they have fallen out of favor with the new style of smart isolators. I keep reading about the massive wire people are running, like 0/0 and 2/0, but you did it all with 6 gauge, glad that that is still feasible. My son sews for… Read more »

Eric Lei

Hi,Good job and thanks for your information.
Just wonder , what model of promaster you had converted ? 2500 or 3500 ? And what is the wheel base of your van?
It seems you don’t have any bathing facility in your van ?
Thanks
Eric

Hi Eric!

We have the 1500, 136″ promaster.

We use this solar shower that we hang off the back of the roof rack and if we want privacy, we open both rear doors and hang a shower curtain in between with velcro.

As for a toilet, we’ve never had any issues finding bathrooms while on the road or camping, but sometimes when stealth camping in a city it can be more tricky. There are many products people we’ve met use, like a folding toilet or this product for women that can be used with doggie bags.

Sascha Güssler

Hi 🙂 Building out the same van I was wondering what the dimensions of your bed are and if you are happy with the size?

Thanks a ton, Sascha

The bed is a full size bed, 74″ x 54″. I would say if you’re 5’10” or shorter, a full-size bed is perfect and will be an exact fit between the beams in the rear section of the Promaster. If you’re taller, I would lift the bed platform a couple more inches into the side panels where windows should be and not add much insulation on the sides – that way you can fit up to a queen size bed across. If you get the foam mattress we suggested from amazon, you can easily cut a few inches off the… Read more »

Sascha Güssler

Thanks for your detailed answer. It’s much appreciated! That’s pretty much the dimensions I had in mind. I’m from Germany, an found a store that makes custom-sized mattresses for just a little more money than a buying a regular one. Pretty sweet 🙂 One more question: Since I pondered a long time with the roof height, are you happy with the low roof? Or doing it again would you have preferred to have a higher roof? I chose the low roof since it make for a cosier build in my opinion, and not being able to stand up tall wasn’t… Read more »

Connie Ulrich

An amazing job on promaster! Best information I have found! I just bought one exactly like yours! So on the vinyl flooring have you used glue to hold it down? if so what! Thanks for sharing all the details of your build out! I know it took a lot of time.

Dennis

Please explain more about the install process for your battery vent. Pictures?

We drilled a 1″ hole near the very top of the side of the battery box, facing the rear doors. We also drilled a 1″ hole in the van’s sheetmetal right below the taillight, and this hole is seen from the outside if you look through the gap where the rear door hinge is. It’s pretty hard to capture in a camera because it’s inside the rear corner pillar. We then used 1″ clear tubing to connect the two holes and used sealant around the holes so it’s sealed pretty good. The gases created should exit out the tubing, into… Read more »

Rodrigo

wow…very nice job, congratulations

Thank you!

Arne

Really nice looking van. I just bought a 2017 Promaster 1500 136″ Low Roof and was wondering how you did the roof platform. Did you attach the platform to a roof rack, or did you make your own rack?

Thanks! We made our own out of 80/20 tubing and made some mounts that slide in over the factory roof mount stubs. I’ll write something up about how to do this soon

Beverly Robin

WOW. Good to see a complete walk through on Do It Yourself custom van conversion. You are now expert to do any RV/Camper Maintenance as well.

Julie Ann Robinson

Nice build! Wondering what your setup is for eating in the van as there appears to be no table or chairs.

Scott Johnson

Hi guys,
I’m looking to buy a Promaster and start a build, my question is have you ever regretted not getting a “high roof?” What were your thoughts on purchasing the standard van? Any input would be greatly appreciated.
Thanks for the help!
Scott

We bought the standard roof version because we got a great deal on it (20k for a basically new van) and for us it was the best model since we planned on going places where height restrictions were common. It has worked out great for us since we can get into most car garages where the high-roof version wouldn’t fit, and since we’re only standing in the van for short periods while we cook or move around, the lower interior height hasn’t been a big issue. However, if I was buying and converting a brand new van for use mostly… Read more »

Timothy R Gillespie

Did you put any info or videos on where and when to run your wiring? I am having a hard time deciding where exactly to pre run wiring.

No, the placement of the wiring is so individualized depending on where you’re placing your components: the batteries, fuse block, solar panels/controller, and all the things you plug in. We tried to run as much of the wiring as we could in the beams of the van and where we couldn’t we used a black wiring loom to protect them and group them together.

Sharon

Amazing conversion, great website – and so easy to understand! Thank you!

Thank you, glad you found it useful!

Nick fairman

Super informative!! Was wondering what you used for siding on your walls after putting in the hard foam insulation boards?

We didn’t use anything else, we just put cloth on one side of the foam and glued the foam to the wall. It gives it a nice, finished look, is super easy to install, and is as lightweight as it gets.

Jon

Do you happen to have any additional photos you could post or email me of the walls? That is the one part that I am struggling with. Also, what are the dimensions of your sliding door window you put in? Thank you!

Henrik

Hey 🙂 Great conversion! But where can you get slide windows for 30$? I found the one you have for 300, did you forget a zero?
Thank you, hope you are travelling nicely!

Debbie

What wheelbase did you get in the standard roof, 136?

Yea, our van is the 136′ which is the size most people choose, it’s a good compromise of interior space and driveability.

Debbie

Also, does your van have dual sliding doors, one on both driver and passenger side? If not do you wish it did or are you glad you only have 1? Thanks

No, ours just has a single sliding door on the passenger side. We rented a van in Iceland that had sliding doors on both sides and it was nice to be able to open it to fill the kitchen or just get unobstructed views, but definitely not a must. I would imagine it would make the conversion a little more difficult too since creating a finished look around the frame of the sliding doors takes some time. I would say it’s not worth paying extra, but if it’s the same prices it’s a coin flip.

diana

Amazing. You guys make the electrics look so easy. My boyfriend and I are thinking about converting a van into a campervan and electrics scare the heck out of me 🙂

It’s really not that hard once you understand how it works. Everything has a positive and a negative. The negatives all gets connected to the metal of the van, including the battery. The positives all get connected to the battery’s positive. The more power a component is going to draw, the bigger the wire it needs. Since it’s all low voltage and low amperage, you really don’t need to worry about things like getting electrocuted and you really can’t mess it up too bad. Just remember to test it all before you enclose it behind panels, otherwise you’ll have to… Read more »

Carol Crosby

Great job.

BEATRIX

so cool, great job! we want to do something similar with a ProMaster City, much smaller of course but hopefully do-able 🙂
great idea on the window addition, where did you purchase a roof fan? also what did you use for the wood slat ceiling and how did you mount it?

Thank You!

The roof fan comes from Amazon, you can click on the link in the article and it’ll send you to the product on Amazon. For the ceiling we used 1/8″ wood paneling but if I were to do it again, I would use something thicker since it ended up warping with the constantly changing temperature and humidity. To mount it, we just screwed it into the ceiling cross bars on the van.

Maggie Houseknecht

Hello, I am currently looking for a used ProMaster to convert. What year was yours and size? I am JUST starting so I am trying to get a gauge of what is a good deal. Any tips are appreciated. Insulation is big for me being I’ll be doing all weather. Are you happy (no mold or condensation issues) with your choices and would you do anything different in any area of your conversion? Sorry, I got my answer about your van from the comments. Note to self, read the comments first. I love learning from many blogs, youtube the “would… Read more »

Hi Maggie, our Promaster is a 2017 136″ standard roof. We used hard foam insulation throughout and we didn’t have any issues with mold. We didn’t insulate the floors much and they would get cold but a small rug is all we needed on really cold days. Also, the windows allow a lot of heat and cold to come through so I would make insulated window covers. Overall, we were pretty happy with our conversion and wouldn’t change much if we were to do it again. Good luck!

iliana

I’m wanting to build a van and use it full time, in all weather. what did you guys do for heating? would it be a lot hard/ more complicated to install a heater/ water heater combo into the van?

We didn’t have a heater in our van so when the temperatures dropped, we used a thicker blanket and a rug on the floor. Webasto now makes a gasoline heater, the 2000 STC, which is really nice but it doesn’t heat water. The Webasto doesn’t seem very difficult to install since it’s easy to access the top of the fuel tank from right between the front seats. Good luck

reiyos

I purchased a promaster and I don’t know where to make the positive connection to the battery. Seems to be a lot of junk under the battery cover. Where exactly did you make your positive cable connection on the vehicle battery? overall, you did a nice job with your descriptive information

reiyos

wait. maybe I think I see it now. The positive terminal with the mega fuse. You did mention that in the writeup. thank you!

You got it, the big black fuse in the picture with the big red wire coming out of it is the connection I made.

Nick

Hi I’m looking into doing the wiring for my promaster with isolator.
What gauge wiring did you use from battery to fuse to isolator ? And from there to the battery. Also where did you make the connection on the promaster for the main car battery ? The picture seems like you go under the rug to the hood.
Is that correct ?

We used 6 ga wire to go from the main battery, which is just in front of the driver’s seat, to the isolator, then back to the house batteries. The top of the main battery has a plastic fuse/distribution block with a blank spot where you can use an inline fuse to hook up your wire. You can go with 4 ga if you’re worried about voltage drop but we never had any issues.