I don't understand the humidity problems, I really don't. I coat in my super-humid, super-hot shop that holds moisture like a sauna, using the shake/bake airsoft BB method and plastic food storage containers with silicone seals and snap-flap lids and it doesn't matter what the weather is, it works.
After about 20 batches I pour the BBs out and dump the teaspoon or so of powder and bullet dust out because the bullet dust accumulates and inhibits the static cling. After that I put the BBs back in, spoonfull of fresh powder, bunch of bullets, and get busy again.