POLL-Paint or undercoat?
Clean it super great to bejesus and back, then epoxy (or moisture catalyzed primer) then body color single stage paint.
Or if on a budget, super clean and roll rustoleum on it. I agree that prep and cleanliness is key. Scuffing, scraping, degreasing, scrubbing w/ soap n hot water etc.
For acoustic dampening products:
http://www.designengineering.com/catalog/boom-mat-acoustical-products
.