This link will help you tremendously...

Simple, cheap, and effective door treatments - DIYMA Car Audio Forum

Lots of good "How to's" are here...

How-To Articles Provided by our members - DIYMA Car Audio Forum

Also, check out the technical area of the forum if your so inclined


Lots of info in this one too...but most get bored/sometimes hard to understand...

http://www.bcae1.com/