They do make plastic drums as well. I am not 100% on this but iI would think they would be less prone to "sweating' and they definitely won't rust.
Could also think about filling them with drain oil, vegetable oil (used fryer oil ?), or something similar but cheap,.
Other ideas: a bagged desiccant (some of which can be reused), and or a small fan to pull air through the barrel, think green house fans on amazon.
Also on the drums, see if there are any drum recyclers nearby as you can get them a lot cheaper. There is one locally called Jones Barrel. Not sure on the shipping cost ?