I know some of you are going to cringe....but I use Herculiner, as a sound deadener and sealer against rust on all my floorboards. No one will argue that it isn't the toughest stuff around but few realize that it completely takes the "ring" out of sheet metal. It stands up to the heat, has no odor and is basically bulletproof. On top of the Herculiner I use a jute pad with aluminized cover, taped at the seams and a rubber mat as the top surface.
I've used Herculiner on a number of off-road Jeeps and haven't had any problems with rust or complains from the owners. It takes about a quart of material and I run it all the way up the firewall. Just another option.
Dave
