BINGO!!!!! my guy that did my headliner suggested the SAME idea!!!!Ya, for the price RAAMmat is the cheepest solution without having to use you own brew.
One manufacter called MFM makes a product called "Peel n Seal" for roofing of mobile homes. Suppose to be available at your local Lowes or HD, but in CA we don't have any. 100sq ft for $90. vs 100 sq ft of Dynamat @$300-400
Hard for me to understand how roofing undermat would turn to goo. I sure the temps on the roof far exceed what the car may experience.Remember that the tar-paper type stuff used on homes has a good chance of turning to goo in high heat. They butyl type products (dynamat, Hushmat, etc) will not.
www.sounddeadenershowdown.com has a good review of some types, but not everything that's out there.
Also possible odor when that material gets hot in summer, or just hot.Hard for me to understand how roofing undermat would turn to goo. I sure the temps on the roof far exceed what the car may experience.