A dehumidifier was asked about. I have always used a Goldenrod accessory in all my gun-safes. A small lightbulb would work, too, but might be easily broken.

http://www.midwayusa.com/product/1138614184/goldenrod-gunsaver-dehumidifier-rod-110v?cm_vc=U112

Nifty-250

"If you don't know where you're going, you may wind up somewhere else".
Yogi Berra