When I used a lamp and a che over my Ball's tank I made a cardboard cut out wrapped in foil to put on the screen. It held in some heat but I am not sure it helped all that much for the humidity. What I did was just keep damp moss in both hides. That gave me great sheds with very minimal misting. The misting was more for the live plants I had in there.
What is the humidity level you have now?