something i noticed when i was using a heat light. if my room humidity was around 60 % my tank humidity was almost half of that if not a bit more. u have no idea how much a heat light dries things out in your cage untill u switch over to UTH.
i frigged with heat lamps for almost 6 months. my room humidity this winter was around 30 - 40 % and i could consistantly have humidity levels in my cage between 50 - 60 % without misting. just make sure u have most of the top covered so humidity cant get out, but still have enough uncovered area to allow air movement. then when your snake is in shed, mist the cage every day (once or twice) and that should get u pretty close to were u need to be. i try and keep my humidity at 80% and have always had a perfect shed. good luck.