What are the temps in the room? I live in Vegas and my 3 larger snakes are in 55, 40, and 29gal tanks. My baby Dumeril's is in a tub. I keep the room at 78-79 degrees around the clock and only use a UTH on all of my tanks and the tub. Humidity in the room is normally around 20%. Cool side stays at room temp or slightly higher and hot spot is 90 degrees. My screen tops are covered with black plastic garbage bag material taped around all the edges with only a very small opening over the hot side for ventilation. I use cypress for bedding, provide a large water bowl, and mist it a few times a week. Humidity stays between 50-70% at all times.
If you just maintain your room temp at around 78 degrees you'll be just fine. Overhead heating with an open screen top is the devil here in the desert....just like the sun and that damn blast furnace wind we get here. Ditch the overhead lamp, seal up the top, and use a UTH on a thermostat.