Well... you're going to be disappointed with many of us, might as well click a different thread lol
Not trying to be DxxK , it could potentially be a very dangerous , especially if vehicle is parked in sun and temps rise so much more pressure.
I'm a chef and member of the Teamsters Union up here in vancouver bc (you have to be in the union to work in film catering here) there are some very stringent rules about propane storage and handling.
They have to be stored in exterior places only ,like mesh lockups, flat deck cages on trucks etc, but not in cube vans, shipping containers or sheds or any vehicle interiors.
I had good friend also chef same job that had propane leak from an oven while he was driving the kitchen to another location. This is 30ft long 19000kg gvw truck mbile kitchen unit. he barely had time to hit the brakes and jump out with his life.
The truck burned to the ground in 20minutes.
My previous camper van had external battery compartment but turned out to have a sealing problem which I found when my battery solenoid malfunctioned while on a highway with nowhere to pull over immediately , my batteries boiled and the air in the van went very bad very quickly. I had to go the hospital because of that. Hence battery comment.
I just want to point out the dangers of internal propane tanks. I would hate to hear about one you guys getting hurt.
I use a portable on demand water heater with a show/bathroom tent if needed for privacy.
If I was building a van I would use the same heater as you , I would just mount the tank outside and plumb a line in with shut off.
Do you have a gas detector in your van btw?
My van does not have gas water heater only a small 12v/120ac instant hot water tank for beverages. The van came that way so I have to use something else.
The portable one have also has tap for washing dishes etc and works well.
https://www.amazon.ca/BaseCamp-Mr-Heater-F235350-BOSS-XCW20/dp/B011TRLWIG