This for sure - I had it in a metal clothes cabinet, the Damp-Rid got saturated, spilled (it was amazing how much liquid there was), and caused some corrosion on shelf. If this happened in a gun safe it could be a disaster.
My safe is in a dry room but it can still get humid depending on time of year and whether central AC is running or not. I have a dehumidifier in room, golden rod in safe (20+ years old), and a couple of these silica gel paks:
One of the most effective moisture absorbers ever developed. These man-made crystals prevent rust, mildew, corrosion, and tarnish before they start by literally "sucking up" and safely holding the moisture that causes them. Yet, the crystals stay ...
www.brownells.com
I still "reactivate" the silica gel paks a couple times a year - I have them mainly as a backup in case the golden rod dies or the circuit trips out without me knowing right away. I do try to check the golden rod every time I open the safe.
This has been foolproof for me over 20+ years, no issues at all.