It's not just humidity that you have to think about but bugs as well.
I also buy in bulk because of the distance that I have to travel to get to a store. I live in a rural area in the South and I would never store any grain products in anything that was not well sealed or around here it wouldn't last long.
There are these little white moths that are everywhere; they are attracted to the lights that shine through the doors and windows. When someone opens the door after dark to go in or out they get into the house. If there is any grain based food anywhere that they can get to they will lay eggs in it.
They get into the grocery stores as well, when I bring a bag on anything home from the store I throw it in the freezer first and leave it there for a couple of days. If there are any eggs in or on the packages freezing will kill them. Then when I remove the bag from the freezer it goes directly into a sealed container.
Honeyville Grain Co. carries a really nice 5-gallon food grade plastic bucket that’s around $10.00. They also send some of those little oxygen absorbers to help extend the self-life of the food. I have several of their buckets and really like them. Wholesale Ingredients to the Food Service Industry, Honeyville Food Products. Premium Corn, Flour, Whole Grains, Sugar and more.