If the fork tubes are rusty in the range of motion, I'd consider replacing them if the rust is causing the seals to wear and leak. Otherwise, I'd steel-woold the rusty areas and oil things up well and forget about it. You're going to get moisture under the gaitors and that will lead to rust. If there are no gaitors, any moisture is going to evaporate before it does harm - think about chrome fenders, they don't rust just because they get wet unless they stay wet.