I have a gun room vault, which I thought was thoroughly dry. Just for kicks I put a couple of dollar store dehumidifiers in there. Two months later they had about 2 pints of water between the two of them.
Grizz
GRIZZ!!!
BEWARE
The Dollarama dehumidifiers I bought for the cold room downstairs apparently contain salts. Personally, I would not, had I known, have ever put those anywhere in my home, much less anywhere near my firearms. Thankfully, I did not. However, some of the items we brought in from the cottage, were not so lucky.
:-(

My $0.02 Cdn.