Thanks RacerX, you answered my questions well! The PA I was referring to is Phosphoric Acid, which I assume your RustMort is and other products like OSPHO.
I was most interested in the treatment of the PA'd area prior to primer obviously.
The issue of the body filler and using another coat of DP over it was to seal it to prevent moisture affecting the filler. I don't know if and when time and budget considerations will allow me to be working on the car, so I have to assume I will be doing parts of it piecemeal until completely ready for the top coats, hence my worries about moisture and rust.
In my situation, I am doing a ground up, with replacment floor pans, fender patching and a rear quarter panel replacement. I will also be removing the drip rails.
I was considering using the DP series primer, which I assume will require a breathing system. My concern of course is rust. After doing/welding each area, I want to coat it with something to prevent rust.
You have stated that you like the POR15 product, and I was considering this for the underbody, but would DP be better? Is there a non-CA product (single stage) that would work anywhere near as well as the DP from PPG that I don't have to worry about carciogens?
Thank You SO MUCH for your willingness so supply us with your expertise.
Brad