Surface rust prep before sound deadning

I spent the last few months researching sound deadener for my current project. Most of the companies that make the stuff sell their thickest material (like Dynapad) without an adhesive backing. When I think about havng a car for a long time this makes real sense to me. Periodically I have the desire to do things to the cars (are they ever done?) and I can see lots of situations when I will be glad to be able to pull the carpeting, removing the floor deadener material and being able to work on something and then put it all back in. For example, welding anything on the floor pan. Everyone is familiar with the stiffening troughs put in the floor board. Even if you use an adhesive material, the chance of getting all that stuff flush on the floor with no pockets is a fantasy. With no adhesive there are going to be all sorts of spaces between the floor pan and the deadener. That is obviously not going to be the case when a well prepped and painted floorpan gets wet. Then if there is some unexpected leak into the floor pan (water, a Big Gulp. leaking heater core...), you can pull all the stuff on the floor out, get the moisture out, dry everything and reinstall.