I did a little write-up on peel & seal and sound deadening a while back. Here's the site:
http://www.cardomain.com/id/turbolaxx
The Peal & Seal works fairly well. I can turn it up quite a bit and let it really thump on the inside of the car. If i get out and shut the door it's really quiet on the outside from what you would expect. It's def the poor man's dynamat. It's only about 1/16" thick but works pretty well. Look in the yellow pages under roofing supply and call them up. PM me know if you have anymore questions about it.