Corrosion of bare steel is usually due to condensation. I would get that in my garage in Atlanta. No problem in my garage in drier California now, but I still get condensation outside under a carport in winter, even dripping from metal rafters. It is due to the temperature changes, which are much less inside. Of course everything is worse with salt. A relative's beachfront house in Florida is already showing a little rust on stainless fasteners outside after just a year, and painted steel parts are horribly corroded.