Hot humid is it down there?? In addition to your dehumidifier rod, swab all iron/steel parts of your guns, including tthe bore, real well with Birhcwood-Casey SHEATH (BARRIER??), then put each one in a silicon-impregnated GUNNY SOCK! This will definitely keep them from rusting!!

I kept my gun safe in the milk room of my barn in central NY for over 10 years, plenty humid, and never got a spot of rust on any of them treated as above. And I didn't have a dehumidifier rod in the safe, either.