does POR15 really stop rust?
 

my winter beater is scabbing on the door bottoms and the rockers...no holes, its solid but rusty...without welding in new steel, would POR 15 over the scabbing, epoxy primer, gravel guard and paint suffice for a few years until I retire her?

The answer is yes and no. It basically smothers it. Google the website.

You need to get to the bare metal for Por 15 to work well. It will not be effective over undercoating and other coatings. The surface needs to be ground down to the metal and you need to get rid of as much of the rust scale as you can before applying Por 15. Like rw says, it doesn't kill it, it smothers it by protecting the treated area from air and moisture. I use a product called Rust Guard made by Wurth. It is very similar to Por 15.

At Canadian Tire, another product available called Rust Stop claims that a chemical reaction actually stops the rust, converting it to a paintable surface. It changes the rust to a blackish brown colour, its very hard then.

I think I'll grind the hell out of it, slather it on and prime, gravel and paint. Good enuf for Betsy.