I use plastic containers for ALL my ammunition, and have for decades -- I mean things like plastic shoe boxes, and bins of various sorts. They seal fine for moisture, and I've never had a problem with any ammo, including contemporary ammo such as .22LR, 5.56, 6.5 Swedish Mauser, Swiss 7.5mm, 7.62x39, shotgun shells, WWII 30-06 ammo in belts(!), etc. This is all stored in a corner utility room that includes our massive whole house water filter. Yet NO problems of moisture or corrosion over about 35 years now.
My multiple pounds of black powder and percussion caps -- both true black and a couple canisters of Pyrodex -- are stored in a large plastic toolbox under a bench in the garage.
I agree that there's a certain historical/romantic appeal of the old steel GI ammo cans, but for storing ammo in your home/barn/shed/whatever environment, I don't see an advantage there.
