You need to control the UTH with something. A reptile thermostat is preferable, but a rheostat or lamp dimmer will do. You will just have to constantly adjust it.
If you have a second UTH, you will set the temperature to 80* (where as the hotside would be ~90*). This way you will have a temperature gradient.
If you get a CHE, you can leave it on 24/7 but it will lower the humidity. There is no way to control the humidity with a CHE other than using a dimmer with it or just turning it off entirely. As long as it is on, the humidity will drop significantly.