Doesn't matter. The ramped heating and cooling down in humid climates will give you this issue no matter how many de-hums you have in your safe. It usually starts after a trip to the range and not cleaning it after wards.Fred, it has been fairly humid the last couple weeks. There is a dehumidifier running the the area I store my firearms though.
The people talking about corrosive ammo tend to forget that the primers are the corrosive part and it usually results in the action area. The gas system rust is usually caused by the rapid heat changes when shooting in a humid climate. Hence why people in the Okanogan of B.C. tend to have less rusting issues than say people in the LMZ (lowermainland Zone)