(We’ll be going to a high humidity area for half of the year, so I’m trying to protect against moisture.)<<<
Why not try to get the plastic buckets that they give away in the cafe’s and bakeries and use them?
Or the new plastic bags that cat food comes in, they could have the tops rolled a couple times and then the roll stapled shut.
My first thought was the paint cans, but the metal and chemicals might not be a good mix.
Of course the off sized jars, that cannot be used for canning would work, LOL, except that I used a lot of those for salt storage.