horse sence,
My worry for Rob would be that he may live in the part of Louisiana that is only one step this side of being a swamp with very high humidity and anything absorbent, like foam rubber carpet pad, might trap enough moisture to rust his roof in short order. On another note, in our HOT climates, I tend to choose "sound deadener" more for its temperature barrier/insulation qualities more than for its sound deadening factor. I've had OK luck with a product from Home Cheapo that is about 1/4" thick, has smooth aluminum foil on one side and sort of a gummy/semi-sticky grey stuff on the other side. I then spray it and the surface I want it to adhere to with a foam/fabric contact cement/glue, let it tack up for a few minutes and install. I'll see if I can get you the brand and product number of the stuff from Home Cheapo.
Just My Thoughts,
Gene