DIY van insulation - success stories?

[boardrider247]

Currently looking for guidance for insulating my fiberglass high top. Thinking of gluing 2 layers of 1/2" foil backed foam board in place with possibly a 1/8 plywood interior.

Thoughts?

If you can get your hands on it I would use a closed cell rubber insulation. Armaflex is the most common brand name. The insulators at my work use it on large tanks and buy it in 4' tall rolls. Up to 2" thick I think.
No idea where you would buy it at a reasonable price off the shelf though.
Maybe a few of those cheap asz walmart camping pads? Essentially the same material