Soundproofing Road Noise

I used "Lizard Skin" inside the car and DUI overhead and on the firewall . the underside is painted and clear coated because it's easier to keep clean . they are both GREAT products . Do NOT use the products from the home center ! Most are asphalt based and you can't get the smell out . You don't need undercoating unless you drive your Mopar year around .
Second Vote for Lizard Skin. I sprayed their Thermal barrier and Sound barriers on a friend's 67 Mustang, and I was very impressed. Going forward, it is all I plan to use.