Your link doesn't work, but sounds a lot like David's syncro mod. I believe he used a waterbed thermostat to control the thing. I never liked the idea of heating the water inside the tank, as it tends to contribute to biological growth. That tank was never really designed for heat either.

What I have done recently is to use the Eccotemp. This is an instant hot water on demand. It hangs from the gutter of the van and using an extend a stay on my propane tank, I made a connection to the unit. I put a special non-spill valve in the city water port, so that water goes out instead of in. A flojet pump completes the package. The flojet is a pressure activated pump, so that when the unit is turned on outside it instantly starts the pump. I went one one extra step and routed a line back into the van so that I could get hot water on demand at the faucet as well.

While I spent weeks designing the contraption, the final installation turned out to be pretty simple. Much less involved than monitoring water temperatures and such. In 5 seconds you have hot water at a consistent temperature with good pressure.

I can take some photos, if you or anyone else is interested.

Troy