Why a humidity issue? because of the screen door?
My WD has a screen door on his temporary cage and i thaught it would cause a humidity issue, but so far his humidity stays between 60 and 70% which is a little low, but he sheds good and no problems have accured and hes been in there for about 6months.
Note thats its way smaller than what you have so i dont know how it would differ.
A humidifier or mist system would definetly take care of it tho.