I have used this http://www.metalshield.com/
and for $50 plus shipping its a bargain. Insulate sound deaden and rust proof with one product.
From the website: This product can be used as a single coat system or a two coat system. When using a two coat system a "wet on wet" application method is recommended.
This can be achieved by applying one coat of METAL SHIELD at 5-6 wet mils, let flash for two hours and apply another coat at 10 wet mils.
It can be brushed or rolled on, I used my critter spray gun.