Rust is a bad omen, it means you need to give those misbehaving firearms to me for safe keeping...
On top of a dehumidifier, an old timer told me to soak a rag in rust preventative oil and leave the rag in the safe. Re-oil it twice a year. That and wipe down the guns yearly
+ use that rag to wipe down any metal surface after anyone touches them because of sweat and natural oils from hands.
I've never had to re-activate the desiccant.