I keep bikes in an unheated garage in Maryland - the Chesapeake Bay on one side and the Atlantic Ocean on the other. We are quite humid in the summer and often in spring and fall. I don't see corrosion problems with the bikes because the inside temp is only a few degrees different from the outside temp. The garage has a vapor barrier under the concrete floor, so that may help.

IMO if you want to heat/cool your garage, do it year round at a constant temperature.