from personal experience is modding cars and doing sound competitions Hushmat is by far the best sound dampening material out there. It sticks to any surface unlike most where you have to clean clean clean. A full car install will run roughly $1,000 USD and is so quiet its like riding in a lexus and I was pushing5000 watts of power in my last car and you almost couldn't hear my system with the windows and doors shut. Hushmat was originally used by GM in specialty vehicles proven to stick and stay even to the inside of dirty greasy doors in the factories.
