I use a polyisocynate foam board with aluminum foil on each side[R-max]...it's $10.00 per sheet[4X8' at 1.5 inches thick with a "R" value of 15....cut it with a razor knife-box knife or carpet blade....score and fold then cut the backing just like drywall....glue in with liquid nail and hold in place with carton tape till the next day....foam fill gaps with spray can foam....it won't squeek. Make sure you cover it with a fire resistant finish such as alminum or maybe a flame resistant panel....finished, it's overkill but you will be more confortable-and won't need so much heat/cool....If you can't get 1.5 inch use two sheets: one 1'' and the other 1/2 '' or two 3/4"....ask store for a discount on janged sheets that are busted snagged....I saved at least 50% that way....The better the job foaming you do, the better the insulation in your coach....some reefer trailers are spray-foamed with polyisocynate....thats the best way to do it...costs about $1.00 per sq ft per inch thickness it's "R" value is 10+ per inch thickness because of no air movement what-so-ever any foam will not decay-shift-settle if it is covered and the sun can't shine on it....heat won't bother it if there is a radiant barrier....geof
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