My experience in the SE is that anything that can rust..WILL RUST!
Everything made of metal in a barn rusts over time. The problem is those cold Spring and Fall mornings where the morning temperature and humidity rise real fast. We can have snow at 7AM and then 70 degree temperatures by Noon. The bikes and everything metal are still cold, and they get soaking wet with condensation, just like a glass of ice tea on a summer day.
I would definitely treat the bikes with silicone/oil and then try and seal them in an air tight plastic bag to prevent moisture from getting to them.