A 'Golden Rod' functions by heating the air inside the safe slightly thus reducing relative humidity.

Condensation is caused by the temperature of an object being cooler enough than the surrounding air to cool air in contact with the object to below it's dew point. The dewpoint rises or falls with relative humidity.

That's all there is to it. Obviously, the more stable is the temperture and humidity in the room containing the safe, the better.

"The price of good shotgunnery is constant practice" - Fred Kimble