Wanted to add that the ultratherms look basically like heavy duty laminated heat tape.. So very thin and easy to put a thermostat plug between them and the bottom of the tubs. Also, they come in "strips" that will heat + tubs with just one plug. I'm currently using an ultratherm strip to heat two 32qt tubs side-by-side. It works pretty well, but the temp varies slightly on either side of the UTH (about 3 degrees).

They tend to heat up more evenly than other UTH and appear to not continue to heat once power is shut off, which had not been my experience with other UTHs. I am currently using mine with a hydrofarm (a non-proportional thermostat) and it is working well.

I agree with Deborah that they seem to be very durable. You just have to watch out about bending them. Other wise, I can wipe them off with a damp cloth, Peel off the foil tape, and store, reuse, etc.