I have a layer of Dynamat on the underside of the interior on the rear hatch, and also a layer on the exterior door skins and the interior door panel. Although the installation process is simple it will take a while. Getting a good bond between the mat and the sheet metal is the key to making work well.
It does work well. I did notice less road noise through the doors after installation. I also have far less rattle due to the sound system, which is why I installed it.
There are many different brand names out there, but last I shopped around they were all about the same $.
Good Luck
jason