-
@Cadgirl, I live in Nebraska with a mid-West climate similar to Michigan and my guitar area has been in the finished basement for years. My experience has been that humidity is more variable in the basement both winter and summer. I have a whole house humidifier but augmented it with a room humidifier in the basement room where I store my guitars. In the summer, even with the air conditioner running, the basement is noticeable damper than upstairs. But my guitars have easily survived in the basement with no problem.
Having said that, I’m in the process of moving my guitar area upstairs to a spare bedroom. Besides the more stable humidity level, that bedroom is the quietest area in the house (furthest away from the furnace).