Glass enclosures are hard to hold humidity. With that said first off you want a heat pad for sure on this tank. I currently have a glass enclosure, about to go different route, and I use a UTH and also a heat lamp. My top metal screen type lid I wrapped in tinfoil and then used hvac tape to tape it down. I put about a 1/2" opening around the light opening so air can vent out. This has helped a lot with humidity but still not as good as a AP cage.
Personally I would look into a AP cage, if you can not afford yet then just start saving, you'll be happier in long run. This is what I'm switching too this week.
If you want glass there is a thread on here showing how someone modified a glass tank to work better but you'll always fight with humidity.
Working on getting the money for a heating pad at the moment. But in the mean time, i have a heat insulating sheet around the lamp on top with room for ventilation and have increased misting water since he has now gone into shed.