Found Some!
Well, after searching at numerous stores including Lowes I found a distributor for Protecto Seal just down the street from my office. They sell a ton of this stuff just for the application we're talking about, soundproofing. The stuff I bought is "Protecto Seal 45 Alum," it already has a relatively heavy guage aluminum backing on one side, perfect. The guy says it just keeps sticking better after it gets hot, just like Pilotman proved. Haven't installed yet but this has to be the easiest/cheapest way to go. Here's the lowdown:
Sunshine Supply Co. , San Marcos, CA, (760) 471-9008
12"x50' roll $38. 80, 6"x 50' roll $19. 40. This is inexpensive enough even if you had to pay shipping, those 2 rolls probably weighed 25lb. - 30lb. I'll let you know how the install goes when I get to it.
Tom