Ok, i've got my tub set up with uth and paper towel substrate. But today I moistened the towels and with uth the sides of the tub are fogged up, humidity reads 99%. Without the uth the humidity was 70-80%.
What is ideal?
The heat is causing condensation I would assume. Try lowering the amount of water/humidity. I'm not sure the exact level but from what I remember it's around 40-60 so that may be high but double check that.