Whats the best way to sound deadin the back seats?

I just installed two p3's behind my back seats and am getting some vibes from all the metal in the back. I was going to put in dynamat, but is there a better and maybe more cost effective solution?

 

My neighbor had installed a wood floor in his house close to the time I installed my sub cabinet and he had a bunch of left over self adhesive foam floor padding that goes under the wood. I put that stuff on the inside of the plastic and it totally killed all of the vibration coming from the seat back. For the metal wall and floor around the sub I used spray adhesive and this gray dense foam floor mat from Lowe's that's normally used as a work station floor pad. You could also use some kind of carpet.

 

www.sounddeadenershowdown.com

If you opt to buy elsewhere, at least read through all his stuff. Don is one of the most honest in the business about what this will and wont do for your ride, and knows how to get the most out of it.

Then, check out this thread:http://www.tacomaworld.com/forum/audio-video/59941-my-deadening-project.html