All the above. I would strip the Quarter like said and see what you're working with. If you need wheel house or trunk extensions it is easier to do if you plan a quarter skin and have the quarter off for access. And in the end it makes for a cleaner job and less work that doing multiple patches on the same panel. Like said common for the inner rocker to be rusted out behind the quarter. Clean up, treat metal with Ospho or Rust-Mort as you go, buy a hand held spot blaster. As far as spray bomb primers it will not protect the metal nor will most 2k primers. Rust can breed under the primer. Epoxy is about the only option for a primer if you're going to let it sit in the weather. Also spray can products/paints can cause issues when it comes time to put a real paint over them because they are not catalyzed therefore not inert to solvent penetration or stable. Fisheyes, lifting, or other goofy reactions can occur. Some guys use them and get away with it but I've had it bite me more often then not. Any rust left behind will breed all over again. If it's in a garage and been stripped I use etch-prime, again not the spray bomb stuff. A little goes a long way. A quart will cover a whole car and keep it from flash rusting while you go around it doing bodywork etc and a lot of 2k primers and some epoxies want an etch prime on the bare metal anyway.
