You really need a thermostat to regulate the heat tape, that's asking for an injured snake. The price of a thermostat is nothing compared to vet bills. Not only can it injure snakes but the tape can get extremely hot even start a fire hot so I would not risk it at all. And yes back heat is what you asked about originally.

As for the humidity drill holes in the tubs to get some airflow, add a few on each side and add as many as you need to get your humidity at a good level. Remember you can always add more holes but you can not remove them so take it easy.