I use Purina Layena, and vary from 3-6 hens at any one time. A 50# bag lasts me a long time, easily 6 months. I fortunately have never had a problem with bugs or mold or off smells.
I use rubbermaid garbage cans. I have 4 lined up in the shed, layena, scratch, peanuts, BOSS, wild birdseed, and a couple other things that slip the mind right now. The squirrels have chewed holes in all the lids, going after the peanuts; so the Layena and scratch is not covered and the bag is open. I think the coolness and air circulation helps, with the dampness. Might be a different story if I had to deal with heat, humidity, or rodents.
Imp