I'm thinking of insulating my older van with 3/4" or 1" foam insulation panels with a foil face. This would be glued in place with some 3M spray adhesive. Would this be a good way to go or would it be likely to hold moisture behind it and cause rust?

 

it seems to be the prefered way . I think they use thinner stuff though ,

 

Use thinner the thicker will not conform to the panel walls. Maybe a couple of layers of 1/4-3/8 no more than 1/2 inch to use. Thicker might work on headliner and floor as they tend to be flatter

 

General rule of thumb is foam is preferred although there are other materials well suited for this with a little work foam can be cut to conform to the cavities in which it would eventually be installed.

The first consideration will be deciding how you'll cover the side walls and ceilings in order to determine the cavity depth which in turn would dictate the foam panel thickness used. Roof/ceiling would be no more than 1" thick if you're using the factory roof bows or supports as the "nailing surface" for final trim. Sidewalls could use from 1" to 2" depending where along the horizontal plane insulation and covering will be applied.

If there's a "trick" to having thick foam panels conform to the curves its simply cutting them into short sections that lay almost flat against the sheet metal. If you're familiar with woodworking this would resemble vaulted ceilings or other glue-ups where the finished result is a curved surface.

Sadly I don't have any illustrations to demonstrate this. For my own insulation of a work/cargo van I used a combination of radiant barrier insulation along with traditional fiberglass unfaced bats, the Johns-Manville white no-itch version. Works well enough to be comfy-cozy with my after market rear heater----tee shirt only warm even in winter.

 

I put 2" thick boards in the walls of my 73 Econoline, left a 1" gap for air at the bottom of my walls, to allow it to breath, just slit it with a utility knife for relief cuts to allow it to conform to the wall.

 

I have some cabinetry woodworking experience, so I think I know what techniques you guys are referring to.

The insulation panels I was looking at at the big-box home improvement store were already "pre-bent". Someone stacked the panels incorrectly making them all bowed enough to only require a few relief cuts where the body curves the most! Hard to beat the convenience of pre-bent.

I guess I'm concerned about the lack of air circulation between the insulation and the body. I think I'll just Por-15 the whole inside before I install anything.

 

Before you go all crazy with POR-15'ing the whole interior consider this.....

Adding insulation and then perhaps interior finish trim paneling the need to protect body sheet metal from condensation disappears because after such improvements it no longer collects on the sheet metal. Since the finished interior is now the first surface condensation would reach if it were to collect anywhere it would be there.

Because of this moisture isn't trapped in insulated cavities its not necessary going to extraordinary measures to stop something that doesn't happen.

 

If you're gonna use the thicker foam, then you could cut it all the way through for the relief cuts, but I would just use a box knive and cut at 3/4 of the way through it so that you can make it "flexible"