Dynamat Extreme.....
Although this will certainly not help with the MPG's, my wife may ride in the car with me now. The road noise and the noise from the Magnaflow exhaust made it hard to have a conversation. This is 36 sq ft and it was $150 off of eBay. I used every inch to get to this point. I chose the Dynamat because you do not need a heat gun to install it. I had never installed it before and wanted it to be as simple as possible. I may do more of the car down the road, but this will take care of most of the noise.
The trick is to get the area you are installing it on clean. If your car at one point in its life was a rust bucket like mine was, you will have lots of dirt and dust in all the cracks and crevices. Also in those cracks and crevices, I found some rust spots I could not see from the outside. Some of them I could not get to, so I sprayed them with a rust killer the best I could, then covered them in bedliner, then on some of the spots I could reach I also added short strand fiberglass resin as a final step. I looked at videos of people using rollers to get this stuff smooth, and while the roller worked ok, I found that a tennis ball worked better.
