but also DON'T put a cold gun into a safe with a Goldenrod in it or condensation can occur on the gun & especially IN it! Let the gun sit for an hour or so to assume roomtemp then put it in the warm safe)
Here in Phoenix I have the opposite problem. My safe is in the garage and in the summer time the inside gets pretty warm. And no, I do not use a Goldenrod!
A box of desiccant works just fine here.