I know how that is. I was in Teagu and Pusan over the summer, Terribly humid.
If you want it to just be a bare steel appearence with no rusting then use an oil of some kind. I don't know if you guys have it in Korea but I have brushed wd-40 on tons of parts before. A couple years go by and the part is still rust free and does not have the appearance of being coated.
When I wanna paint I take great care to ensure the part is throughly cleaned and I have no problems with fish eyes.