I use Golden Rods and the cheap dollar store dehumidifiers.
The combination of the 2 keeps the humidity level right at 45-50% which is the recommended level of humidity in the safe.
I have 2 of the temperature and humidity gauges - 1 in the safe, the other in the room with the safe. The rods can fail and a quick check of the 2 gauges will let you know.
The cheap dollar store dehumidifiers need to be checked at least once a month. You will be surprised at how much moisture they absorb even with a dehumidifying rod in the safe.
