Tank heaters are pretty standardized. Just a pad glued to the tank, and a thermostat. You add your own on/off switch.
I went with the Ultraheat mentioned above because they were AC/DC. When I was plugged into shore power, all I had to do was flip a breaker. They were much higher quality compared to the other offerings at the time of my install, which was 2004. Other heat pads were foil, Ultraheat were a rubber mat with better glue.
I also added a 12v only heat rope wrapped around the tank drains near the gate valves.
Dunno if this was helpful or not. JMHO
