I lived in Charleston SC many years ago on one of the barrier islands. The ocean breeze WILL rust any exposed steel. Even a painted steel bike is susceptible. If you have the wherewithal to remove the headset, crank and seat post you might consider spraying the inside of the bike frame with a sealant. Some bikes shops down there may have it. I know the online shops do.

I had a nice Raleigh when I lived down there and after a couple of years even being inside it started to rust. I pulled the headset, crank and seat post and the inside had light rust but no pitting. I found the key for me was to lightly spray the bike down after every ride, dry it off and take it inside. After I started doing that the bike didn't seem to rust much more than it already had.

The salt air is just something you'll have to deal with. I'd highly recommend going to a good bike shop in your town and ask them what they recommend.