On one of my tanks (20gal) I use an overhead basking light and a screen top, had a rough time getting my humidity right, what I finally did was went to a local home improvment store and bought a piece of plexeglassthat will cover the top. I set my water bowl on part of the UTH to create humidity, if the humidity is too high then I move the plexeglass more off the screen, humidity too low then I move theplexeglass to cover the screen, during times of shed I take a towel wet it and ring it out, put it on top of the tank all the way to the basking light and then put the plexeglass on the towel. It works great! Hope this helps!