Dynamat ($$$), and I "found" a material called "Safseal" made by a company called Protectowrap (really). They make a building product called Jiffy Seal which is recognized in the building trades as virtually bulletproof. Anyway, this safseal is a clone (or vice versa?) of Dynamat: 60 mil thick, self-stick with an aluminum foil face. It has no asphaltic content (no smell) and the best news: I ordered some from a builders supply for $.80 per sq. ft. (and not a huge order: 120 sf). The guy at the shop said he sells pallet-fulls for this exact purpose. So I'll follow up with an install report. Those interested might want to do some on-line looking