The Stovebolt Site Forums The Shop Area Paint and Body Shop Under Coating

That's probably equivalent of what I used for undercoating. I used a product by UPOL in aerosol cans. Seems to do OK, but what you're putting it on has to be clean. I used some black adhesive foam sheets inside the doors and on the underside of the roof to help deaden the noise. For noise reduction, the more mass that's there is better. Even a blob of tar will help the doors go clunk instead of clang, but that's smelly.