Hm.. have you tried covering the screen lid with saran wrap instead? (of course, not letting it get too close to the light, which could melt it..) I would advise scrapping the lamp; they dry things out.. is there any other way you could heat the room around the cage, like with a space heater? It is a bear, getting temps in glass tanks to be right, I know.. maybe set up a tub and sell the tank? Tubs hold humidity like a dream.. even too much sometimes so that holes need to be melted into the sides.