Scamp gets the insulation number from the Reflectix published numbers (and the other stuf they use also), but it really depends on the orientation. It's a double-foil with bubble-wrap in between, and then the marine carpet, aka rat fur, is installed on the inside of it. So, you have fiberglass, Reflectix and carpet.
Larger wheels might not fit; even if they did, your 'bounce' room would be shortened. If you want extra room for larger wheels, have a spacer welded between axle
bracket and frame.
BTW, I dragged my 91S13 all over BC, YT, AK and some of NWT with 13" wheels and had no problems, but on the rougher roads, I lowered the tire pressures on truck and trailer to make them less susceptible to rock damage and I also slowed down. I didn't go on either the Dalton or Dempster Highways.