Never had any problems with a guitar up in the mountains in Colorado in winter. I had a cheap one which I'd leave up there. It'd go down to 20 below or more while we were away and we'd get the cabin toasty hot when we were there every weekend. Humidity was also very low, below 10% most of the time.

The only problem I had was, someone broke in and stole it. I hope they enjoyed it. It cost me $14 at a thrift store. 'Course I had to fiddle with it a bit at first, to make it playable.

Then I got to carrying my Yamaha back and forth. It didn't seem to mind being in the back of the truck on the journey.