I'm not finished sanding yet, but when I do there will still be rust left. Here are the products I will be using and then some pictures of the rust spots. One is about 2 inches wide, the other about 1.5 inches.

 

Only thing I know is that if you leave rust, any rust, it comes back.

 

I hate body work mostly because I hate corrosion. I was gonna say you need to cut the metal back a few more inches so ALL the rust is gone. That primer you show is probably not a rust-inhibitor. It's just a primer to help the paint stick. Spray that primer over the rust-inhibitor.
I've heard good things about POR-15 but haven't used it.

 

Okay, thanks. You probably just saved me the hassle of having to do it all again in the future. I just assumed because the can said "Stops rust" that the primer alone would work.

 

Maybe it does, but I'm pretty jaded about those kind of claims. Not really down on RustOleum cause they seem to make good stuff. Just think you should look for another product that really says rust-converter or rust-inhibitor.

Rust-inhibitor is good if you can absolutely grind back to clean fresh shiny metal. Not sure if you can because you probably cannot access the back-side of that surrounding metal, and it looks like a couple different layers of metal overalapping. Say if you were to replace the entire quarter-panel.

Rust-converter changes the rust over to magnetite (black stuff). Then you put primer & paint over that. Still, complete success requires that you paint the stuff over the backside as well as all layers, etc.

Rust sucks.