Wow, I can't believe nobody caught this yet? If I'm wrong I apologize, but you said your enclosure is wood but you didn't say if and with what you sealed the wood with??

Your biggest problem could very well be the enclosure itself not your husbandry. The wood will literally suck any and all moisture from the tank unless sealed properly.
You need to use a good acrylic wood sealer and let it set and dry for at least 48rs. After 48 hrs let it air out for another day or 2 to make sure it's set and dried properly. Once dry and set it will pose no harm to your pet.

Hope this helps.
Gavin