I'm wondering if instead of another UTH you might want to get a radiant heat panel and put it on a timer and t'stat for the ambient temps for the evenings.
Gosh, this is really a tricky situation.
In the summer where I live day time temps average around 80-85F and drop to 35-40F at night. The ball pythons are all in the warmest room of the house to help with their ambient temps at night. My boas all get RHP's since they are in the living room where it is chillier.
I'm thinking that a combination might be best for your situation- though I am far from certain....![]()