When I was going through a divorce many years ago, I stored some 1970's pins in an unheated, drive-up storage unit. They were there for 2 Winters. Temps got below freezing and Summers had a fair amount of humidity.
When I retrieved them, I noticed a few pins had bad planking that I did not remember. (The backglasses I had previously removed and kept with me, so they weren't an issue.)
Lesson learned. I think low humidity and 50F or higher is probably best.