ABS headliner question

I used dynamat on the underside of the roof. It REALLY helps with the over all sound dampening from the roof/headliner area.
It is also very quick and easy to install, as for the rust I scuffed it with a red scotch brite and primed it with a good self etching corrosion resistant primer. Also with a full 3" exhaust with Flowmaster 50's I also used the dynamat in the doors, package tray, firewall, and on the floor. Believe it or not you can actually hear yourself think!