My dad's gun safe isn't opened that often. Over the weekend, I took a look in it to wipe the guns with oil. I noticed that some of the long guns were getting a light dusting of green mold on the stocks, both wood and synthetic. A couple, nearest the wall even had some very light surface rust spots.

I checked the golden rod, which is working fine, and I put two large desiccant packs in the safe to pull any moisture out of the air. My question is, why is this safe having moisture problems when the other safe 10 ft away is fine? I have never had a moisture problem in my safes.

Also, other than desiccant packs, what can be done to prevent this?