1. You need at least 2 hides. One hot one cold.
2. put the water over the UTH and the humidity will rise as the water gets warmer.
3. It takes a few hours with the top on for humidity and ambient temps to stabilize.
4. You should get a infrared thermometer to get heat readings for surfaces
5. You can add insulation to the top and sides to the tank to decrease heat loss
6 Water has a lot of thermal mass and sucks up heat until it reaches equalibrium
David