I put down Fatmat MegaMat first and then Dynaliner foam over that. From what I've read, the MegaMat or an equivalent like Dynamat is really not a sound deadener but more for reducing metal vibration within the car. That's why kids use it to line their trunks when putting in those subwoofers. Keeps the trunk from rattling too much. The Dynaliner foam absorbs more sound and quiets the interior. I went with MegaMat because it's all butyl and doesn't have a stink to it like some of the other sticky products--especially those ones made with asphalt. It sticks very well, too, as long as the surface is nice and clean for starters. Now I have to find some carpeting to put over all of that. There are no pre-cut carpet sets that I'm aware of so I guess I buy by the yard and pull out the scissors. I might actually hear my passenger after I get done.