I didn't think about putting something under it. I just used my laser temp gun and the floor is a ew degrees colder than the rest of the room. Folded up a thermal hunting shirt and lid it under it. Should be a good insulator I hope. Will keep updated and would really appreciate any more things to try. I took some foil tape and lined the inside of the lid hoping it would help insulate and radiate the heat. Considered in the morning if the ambient isn't where I want it wrapping the outside of the tub in it as well. Leaving spaces where the vent holes are of course. Does anyone think that would help?