The normal way to control humidity when drying and for post exposure is to use a tray (normally a cat litter tray!) which is filled with a saturated solution of various chemicals. I recently came across "dry camera cabinets" and have been experimenting with one. The pro's and con's to this approach are:

Pro:
Smaller footprint. These are about the size of a domestic microwave
Cleaner to use (no chemical sludge to try and get back into a storage container).

Con:
Smaller footprint means humidifying larger prints cannot be done. The maximum sheet size the one I have is 15" x 9"
Uses electricity at 5w per hour
Minimum RH is 25%, Maximum is 80%