Just a thought..if its humidity, get a dehumidifier and crank it up. might help..especially in a small room.
As far as me. I just had my tanks off for over a month, Did lots of maintenance, plus some farkles. I live in North Carolina near lots of swamps, very humid wet air. My tanks where about 3/4 full. I didn't vent them. I actually capped every vent opening and zip tied every hose. no air was going to get in. When I mounted them back up, not one single problem. My method my not work for others but it works for me so im gonna stick to it! Good luck and sorry your having to deal with it!