You're going to want to stick the Dynamat to the shell of the car (bare metal). If you think into the obvious places where noise might creep into the cabin (door panels, tire wells on the inside, under the driver and passenger seats, firewall) you should put it there. There are many imitators of Dynamat but, not one has the reputation they do. I'd recommend checking out the website. There's a lot of useful information on there including tutorials on where to put it and it's benefits.