Marsaa111,
You did a fine job, nothing wrong with your craftsmanship, that's good! The suggestions and comments I made wee to the design, no squeaks, secured, economical use of materials that function.
IMO, many DIY builds are over built, there is more wood used than really needed, that adds additional weight, your's isn't bad in that respect, but another aspect is over insulating......many might say you can't have enough insulation, but really there is a very marginal difference that becomes a cost/space/ benefit matter.
I was in a stock van years ago in upstate NY, 52 degrees below with wind, the floor was carpeted and had a heavy rubber mat that went wall to wall, we used a aux gas heater and it burned us out of there, we crack windows for safety and to keep condensation down.......we were warm peeling off the winter gear, even taking our spit bath.
An example too, we'd dig a snow cave about 3 feet deep, lay a tent floor and pack snow around the tent. You're laying on top of snow and with a small sterno stove you can be warm with a good sleeping bag. Cold doesn't rise, and when you break that camp you'll see an icy floor. Dampness is the enemy and staying dry is the priority.
I have found that it's not so much the cold we have to insulate for but the heat, if you're going to over insulate a vehicle start with the roof, then walls and windows, the last issue is the floor.
A vapor barrier is to reduce air infiltration and allow management of condensation, consider reflex glued in place that does a good job of keeping the desired temp.
In a vehicle, every inch you build inside takes an inch away from usable space and in a van, space is usually limited.
The hardest areas to insulate and cover are doors and windows. Weather stripping can help at the door jams, might make you pull harder to shut the door too, which is good, that means you're getting air tight. Lots of ways to insulate a window, you could go with expensive coverings or blankets work too. Hot or cold, these are areas to address. IMO
Most say not to use spray foam like Great Stuff in a vehicle, I agree it traps moisture and can cause rust later on, however, there are spots where it will work without issue. Light fixtures on ceiling and upper walls, wiring holes like tail lights, door handles and a bit around wiring grommets. Not globs of it but spots of it, I put some on a paint scraper and spread it in when it's freshly sprayed, like butter and smooth it out. Any area you use this stuff should be visually check annually for any issues. Interior holes are less of a rust issue and keeps air from moving through framing of inner and outer skins inside. Other products light insulation pads for home outlets can be adapted and then there is always duct tape, LOL. Stop the air drafts.
My GF had a custom van conversion company, these trick or opinions come from experience and I've built a few vans as well, Ford, Chevy, Dodge and VWs. Spend time with the 10th Mountain Division and you'll learn about cold, LOL.
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