Make a cardboard cutout to fit the top that covers a good amount of the screen. Wrap the cardboard in foil to keep both hear and humidity in. Cut windows for any heat lamps you may have overhead..
Also placing damp moss in the hides creates a micro climate. Since your snake stays in the hides the majority of the time it gets the humidity it needs even when the overall tank humidity may show a bit low.
I've used the moss tip a lot. I make it damp and then let it dry out before making it dank again when the snake is not in shed. During a shed I keep it damp.