If in a garage, really hard to control. If in a basement, off the floor and away from an exterior wall. I have a general purpose dehumidifier in the same room as my safe, zero corrosion problems. If safe is in a full time air conditioned space you might not need a safe dehumidifier either.
A good investment is a small electronic thermometer/hygrometer in the safe area to see what the temperature and humidity are actually doing.
Desiccant (chemical H2O absorbing media) have to be baked out from time to time and you have to monitor them. Good for short term dehumidification.
The low temp/low heat Golden Rod dehumidifiers keep the moisture out of the safe by raising the temperature and driving out the moisture (actually the relative humidity goes down).
Too dry and you dry out the wood.