If it's bubbling from underneath the paint, then you might be in with some luck. If you can gain access to the underside of the panel concerned, you can clean up the area with a wire brush, rub any flakes away (I'm guessing it's not that bad yet) and apply some good anti-corrosion gel. Once that's done, you can't go wrong with a liberal coat of inhibitor, like Waxoyl.

Two I recommend are by Bilt Hamber and Ku-Rust. The tailgate on my Saab 900 started to go round the lock; I cleaned it up, applied the rust remedy, and it seems to have stopped the process - and that was back in 2006!

If you can't get behind the offending area, you're going to have to attack it directly, which will involve paint, I'm afraid!