I own a fire proof gun safe and have had some problem with humidity in the safe. I placed a cheep humidity gage in the safe and was surprised at the 50% reading I was getting even with desiccant bags in the safe.
Two months ago I purchased one of these Remington de humidifiers and for 25$ I have been impressed how well it works.
It has a simple gage on it and when it turns red (moisture capacity) you take it out of the safe and plug it into a wall outlet for 12 hours and its good for months.
The first week it was in the safe it turned red but the humidity was down to 20% (the safe had not been open in that time). I plugged it in over night and set it back in the safe. The safe has only been opened twice in the last month and a half and the humidity was below 20%.
I have no idea what a good humidity rate for a safe is but we have been having wet weather which hasn’t changed over that period so I think this simple device is working well.
with Remington's® Mini-Dehumidifier. Uses colorless, odorless nontoxic Water Glass crystals to constantly absorb moisture from the air. Every 30-60 days, the indicator window will turn pink when the unit needs regeneration. Simply plug it in to a standard electrical outlet for 10-12 hours, and the indicator window will turn blue when it's recharged and ready to go again. The average life span is approximately 10 years.