It tough to keep the humidity up with a screen top. It will basically be close to environment humidity.

I started out with my first few bp's in 10 gallon tanks. I found it necessary to use aspen and some dampened sphagm moss in 2-3 areas in the tank. The sphagm is nice cause you will likely find your sheds wrapped around it. I was able to keep my humidity at 60% without covering the screen at all. You may need to cover a portion of the screen with foil or something.