I'd pull out the unit, pull the batteries and let it sit outside the enclosure until it drops to what you think is your room humidity. I'd air out the enclosure at the same time. Once you have a baseline idea of what the room is like that your enclosure is in and the Acu-Rite appears to be reading the room correctly, put it back in and see what happens.

How big is this enclosure and how many holes have you already put in it?