Couple years ago Costco ran a special on some renewable desiccant gizmos. Couple LBs of desiccant, a decent color gauge to estimate how much water they have, and then you plug them into a 120v plug and the heat drives off the humidity, so they are re-usable.
I keep all powder in a large old metal locker, not airtight, but slows air entry. Packs last a couple months and I rotate.
Most desiccant packs can be re-used. These are just easy. Regular one's make you put then in the wife's oven for a couple hours. OK if wife is OK with it. Probably takes more watts in a hot environment, though if you are in a cool wet area, the oven heat is not really "wasted" either. I really hate running the oven in the Summer. Just seems stupid with the AC then having to pump the **** heat back out..... I digress..
I have a relatively wet basement in KC area, during the summer at least. I ran a dehumidifier as well, as all my reloading stuff and some guns are down there. Heated up the basement, but kept the humidity down. During the fall/winter/early spring its nice and dry so long as the heat is on.
For folks that are serious, I went long so to speak. Installed a Mini-split AC unit into my basement. Now my basement is cold AND dry all Summer. Costs less to run than the dehumidifier. BUT, up front costs of the mini-split where higher than the dehumidifier.
So I basically protect my powder stash with 2 lines of defense. I have powder from 1982 that I use for breaking in barrels. Its still fine, but a little dirty (was from the beginning) and I have too little of it to mess with long term load development.
One other thing: NEVER ANY LIGHT EXPOSURE to cans, bottles or whatever you gots.
