We keep a sheet of plexiglass over 3/4 of the aquarium top - to cover the screen and beneath that we keep a few damp paper towels. We also keep a large water dish beneath the lamp as well. Our humidity stays between 50 and 60% all the time.

We have one aquarium that we don't have plexi glass for yet so we have taken a piece of card board and wrapped it in aluminum foil...and still put the wet paper towels beneath the cardboard and that works just as well.

Good luck!