My interior of my 1947 teardrop was "naked" aluminum when I got it 2 years ago and one of the first major projects was adding insulation. I used 3M Fastbond 30NF contact adhesive to glue the foam to the metal. Most common contact adhesives fail at high temps and because the skin of my UPS brown teardrop can reach 140F in the summer sun, I needed an adhesive rated for high temperature use.
Fastbond 30NF is easy to use, has very low VoC (so there's no solvent smell later), and is water soluble when wet (so you can clean up with water). It's also not cheap at ~$50 per quart. I used more than 1/2 quart insulating the interior of my 4 X 10 tear.
I covered the 1" white styrofoam insulation with Hull Liner from these guys
http://www.yourautotrim.com/sigrmahu.html. It soaked up a lot of glue, so I ended up hot-glueing it to the interior of the foam.
Here's a photo of the original interior

And here's after installation of insulation, hull liner, and the forward bulkhead, which hides the spare tire, battery, tools and supports the electrical panel and WFCO converter.

The metal interior walls are a problem in cool weather because at night, your breath condenses in the interior and it becomes very wet inside the trailer. I had a bag of clothes in the storage locker and discovered they were all wet in the morning ;-(
<Chas>
