Cover screen with a towel or duct tape to help hold humidity. Aspen bedding is the worst for holding moisture. I use this coconut husk stuff. Comes in a brick. Also, natural woods help hold humidity better than plastic hides, etc...

For heating.. I use a 75w red heat light on the left side of the tank. I covered a lot of the screen on top, left room for heat lamp and some air. That helps hold heat in the air from heat lamp, and holds humidity. Lightbulbs dry out the air a lot, so I also put heat cord (or heat mat) under the tank on the left side under the heat lamp kinda.. that's her hot side. If you can build up some hiding spaces under the heat lamp it makes a good basking spot closer to the heat lamp. Then a hide on the ground of the tank over the heat mat for belly heat (warm side) , and a hide on the cool side (right side). I also have a moss hide on the cool side for extra humidity if needed. I have a 35g tank. Half the tank has coconut husk and the other (hot side) has aspen bedding. Found that keeps humidity around 70. Hot side sits about 81, and cool side around 74-76 ish. Those thermometers that stick to the side of the tank suck. I got good digital ones from Walmart, and a pet store.. its worth it to buy a good one (and thermostats).

Oh, and I also bought a this (dimmer thing) from the hardware store. It's basically a "light switch) that raises or lowers the wattage to the electrical device plugged into it. I plugged my heat mat into it, and lowered it to about medium. You can adjust that switch to control heat. You can also but a thermostats from a pet store or hardware store.