Not sure about humidity since I live in AZ but I store my sides in the garage which is probably 120 degrees some days. I built a box with 4'x8'x3/4" plywood bottom, 2x6 sides and masonite lid that I hung from the rafters, I did that to keep the leather flat and the light out. Works good for me, some leather has been in there a couple years and still good and same color as when I bought it.