Placing a damp towel on the metal screen can cause the screen to rust.

You should cover the most of the open portion of the screen lid with foil tape, foil wrapped cardboard, etc. This will keep in both heat and humidity.

My tank humidity stays in the 30s. I get around this by placing moss in the hides. During a shed I keep it moist and it creates I nice humid hide for the snake to soak up. During non shed times I allow the moss to dry out before making it damp again. This has given me great sheds.

I like and use this. It can be bought at Petco if you have one local. http://www.amazon.com/Zoo-Med-Terrar...s=zoo+med+moss