I see the extremes. In WY I put two cans of damp rid in the bottom of the safe and replace the product once a year. In Fl, a whole different story. We hardly ever use A/C so humidity is 80%-100%. The best thing I have found is to treat guns with the Brownells anti rust oil, put the guns in the cases with the Intercept technology (made by Boyt, available from Sinclair) and put an old sock filled with Brownells dessicant in the case. Each gun is uncased every two months and the dessicant checked for color change (it can be "baked" to refresh it). The cases are expensive but so far have worked 100% perfectly and a lot cheaper than what I had to pay to have a Sauer drilling's barrel re-rustblued after they got rust spots in 2 weeks in a brand new "rustproof" silicon treated sleeve..
Also found them at a substantial discount from Opticsplanet.
The LE is a shotgun case, the LER a scoped rifle case, all are $49.99 each, just ordered four more LER 46" ones.