Have you looked at this sticky?

http://www.ball-pythons.net/forums/s...ad.php?t=32800

It shows you how to cover your screen with 3 layers of foil and some duct tape. I have done this to my current BP tank and it works very well. I just mist to bring the humidity to the proper level when necessary, usually only once every couple of days or so.

I have heard others use saran wrap to cover their screen tops also with good results as well.