From whom does Rockwood get their tank heaters

What model relay, where purchased?

This all gets back to what I originally posted, to find out what FACTORY KIT Rockwood used to install. No dice from Ultra Heat.

That's why they make relays.

The 2606WS has 4 tanks, and if each tank has a heater drawing 9 amps 12VDC, then that means the panel switch has to handle 36 amps!! That seems impossible?

"From whom??" I am delighted that someone else on this forum follows the rule that one must not end a phrase with a preposition.

But as Churchill said, "That rule is pedantry, up with which I shall not put."

And now, back on topic! ;)

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

My 2011 Rockwood does have the Ultraheat tank heaters from the factory.

I wonder where I might get a diagram of what the Rockwood factory heater install looks like, as in what goes where, etc.

Nobody has answered you yet, so I will chime in.

I can't directly tell you who Rockwood gets their tank heaters from, but there are some choices for afternarket kits.
I was F/T for 2 Alberta winters in my 3 season TT and did some research into the matter. I had a miserable time trying to keep my tanks from freezing.

I forget whose product I was looking at, but it may have been Ultraheat.com. Check them out, they have a good selection of options for what you are asking. They also have pipe and gate valve heaters.

And yes, do the black tank too. It's no fun having a full tank and trying to melt a poopsicle first to dump it. Been there done that.