Especially if you live in a very humid area, like Florida, having a dehumidifier in your safe is really important to help you keep your firearm in prime condition. The water found when you don’t have a dehumidifier will destroy the safe and the firearm—or contents of whatever you place in there.
Especially since most safes are hidden away from the light, this makes it an optimal area for mold and mildew to breed and show up.
You can either invest in a desiccant dehumidifier or an electric dehumidifier, get informed about the two before choosing which one is the right one for you and your situation.