You're probably right. I've used a variation of this myself. The tub I had had a motor to keep the water circulating (avoiding hot and cold spots), and I was able to use a simple, cheap immersible fish tank heater to control the temperature. Proportional controllers are nice, but fairly expensive. Adjustment of things like fish tank heaters can be tedious, but once adjusted they stay set quite well, and I've found them to be quite adequate.
Originally Posted by chuck94022