Just a thought but on the walls why not go with upholstry foam? It will be way less mess, use some spray foam to fill the smaller voids, and skip a spray foam disaster.
The thing you need to be careful with spray foam is that it expands. Because it expands, if you spray it in a place with no room for expansion, it can push the seams of your van apart and even break the spot welds.
Id go with the PVC Dow foam on the floor in the plywood sandwich like I previously mentioned, use the upholstry foam on the walls, then put a plastic vapor barrier on the inside over it to keep any mosture that comes from your breath/sweat condensating out of the foam.
Tuck tape everything, then put plywood (or plexi) up over it, and stain or paint to suit.
Also before you insulate you need to think about wiring, you will want to prewire everything that is going on your 12v system.
They make 12V flourescents, id put 2 of them in the top of the van, also they have 12V LED rope lights, you could put those around the top to give you some nice ambient lighting.
Also things like reading lights, 12v outlets, what all are you going to need?
You need to preplan for this before you insulate and cover the interior in, or you will be taking it out and doing it again.
Check out JC whitney, they have a lot of 12V light stuff, so does camping world.
Also, you planning on any kind of running water in the van or a gas connection for a stove?
On the walls where I have those big flat open spots where I would have to glue insulation to get it to stay before I panel it is one of the areas I decided spray foam would be best. Talking with the guy at Tiger Foam he says it's pretty easy to fill big flat areas like that and to start with less, and I can always add more, and trim to panel. As for the nooks and crannies being over filled and ripping welds apart, I was warned by the guy at Tiger Foam about that. He recommends using very small amounts of the foam in those areas because I can always add more, and the foam will always expand front to back, so he said stick the nozzle in there all the way to the deepest point and give it a quick squeeze, wait, repeat if needed to prevent over filling. Places like my door panels will be ideal for that too because there is just no way to prevent ALL water seepage and moisture.
One reason I want to stay away from foam, and cotton batting in the walls and stuff is just because moisture is so big of a problem in these vans, and these things, even the treated ones, aren't mould proof forever.
As for my floor. I plan on going with your suggestion. If I have extra expanding foam left I will use it for the floor, if not I will go with that Styrofoam stuff.
Funny you mention wiring, water, and gas. I have to figure out how to disconnect all 3 stock dome lights and the aftermarket light switch controlled dome light from the van battery to connect it to my house battery. There is a protective sleeve that runs along the driver side rail of the van I will protect when I insulate, it has space for the wires from my back up camera and anything else I might need to snake through to the front.
All house wiring, plumbing, and gas will be run through the floor. Which is why I like your flooring idea because I can leave space for things. The gas line will run under the van to the propane tanks, but can just as easily run inside the floor to the back. The water lines will be contained to the driver side of the van only running to the sink and back to a gray water jug very close to each other, maybe eventually to an on demand hot water heater on the back door, but again, it can be run through the floor. Electricity is simple, anything that needs 120V will be run off power strips from the plugs on the inverter, no hard wiring, and will be localized to the passenger side wheel well in the back and one plug in the kitchen, the 12V panel will be inside a box over my passenger side wheel well in the back, and pretty much all circuits will be close to it, or can be run through the floor. The only thing coming from the ceiling are the lights, and vent fan power, I can buy some 1/2" conduit and zip tie it in place before I foam and snake those wires through there.
