You'll still want some area open to prevent stagnant air build up. When I had glass, screen top enclosures, I would use warm wet towels (not dripping...but wet) to cover the screen top with enough area for my lamp and a small area for air exchange. I would re-moisten the towels twice a day (morning before work and before bed). The problem with most glass enclosures is they are too tall and have screen tops...heat and humidity rises. I would seriously look at investing in a T8 from Animal Plastics or the lower Exo-Terra Medium-Low/Large-Low (depending on size of your snake). I live in the North Central United States and have also used moistened moss and even placed a washcloth inside the enclosure to help with humidity. Ideally, you want 50%-60% non-shed and 70%+ during shed...that's what has worked for me in the past. Just try not to over saturate the enclosure as this can lead to scale rot and bacteria build-up.