While you may get lucky and never have to deal with theft, it’s smart to install some type of secret pocket for your most valuable items.
Installing a swivel seat is a worthwhile addition because it greatly expands the space and adds some dual-duty utility to something that’s already there.
A Pelican case can be used for extra storage and to keep things outside that you might not want inside the van like a dirty grill, firewood, wet shoes, and extra propane tanks that could lead to potential gas leaks.
Another thing to consider in your build that will help with functionality and stealth camping is installing multiple lights that are dimmable and can selectively be turned on and off for different situations and lighting needs.