Thanks for the input! I've been trying to work out a solution for my tub and right now I think adding a CHE over a hole and wire mesh on the lid and insulating the sides may work best, especially since there are a few tutorials out there and many examples of people who have done it successfully.

Would you be able to take a photo and or describe how you set up your CHE heating and insulation? How tall is your tub and how did you keep the ventilation going with the insulation? Also would a Jumpstart thermostat work with a CHE?