If you can show a picture of your set up would help a bit. I started out with a glass tank, which need modifications. It's hard to hold humidity in with out covering the top of the tank. I taped plastics over the the top except around the light.
I still had to mist daily to keep humidity up. Your gonna want to heat the bottom of the tank with under tank heater regulated by a thermostat.
I also had to switch substrate to repti bark, keeps humidity very well.

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