You just need to prepare the metal better and spray paint will stick, and that will be fine. Sand until bright. Some 180-ish grit sandpaper then cleaning with alcohol or something. If you'd like to go an extra step for added peace of mind, use a rattle can etching primer before the paint. That will bite just a little better but yep lets face it... you'll want to squirt a little touch up there just about every time you jack it up. It sucks that jack points were not on the list of things to include when designing the car.
FWIW, the legendary northern rocker rust starts on the inside, in an area not accessible with the rocker moldings in place (and those are easily damaged during R & I). The answer for prevention of that rust would be whats called internal panel coating or cavity wax, applied with a long wand. It fogs the inside of the structure with a wax / oil mixture that clings everywhere. Maybe a shop in your area could do that, perhaps without removing anything.
