Right now it's not heated....
Hmm....
I am in the wet Pacific NW, shop is one mile from salt water.
Lots of insulation (studs are 2x6) and the attic is pumped full of blown in insulation.
Nary a problem with condensation or rust of any type. Been in this shop 20 years. Previous shop was not insulated and rust was a problem.
Insulate your shop! Put in some type of heat, don't use propane or natural gas, both pump moisture into the area. I have a 5000 watt electric mounted on the ceiling and only have to use it when it is pretty cold. 30 minutes of running the heat and the shop is warm and I can turn the heater off.
