I live on a sailboat where the air is soup and this is what works. Treat the coffee like a dry spice. Only expose a small amount to the room, and keep the bulk isolated from the climate. Put weekly rations in a tight jar. Freeze the rest flat in thin packets so they thaw fast. If your kitchen is steamy, store the jar inside a larger sealed bin or drawer to buffer humidity swings. Do not open containers while they are still cold. Wait until they reach room temp so you do not get condensation inside.