Well, I did it.

Sounds like your 2nd test is a nice option to keep the chill away on boondocking trips while conserving energy.  How often did the WH fire up during the two tests?

SWEET!  There was a discussion on this a while ago and I forgot about it.  I can't wait to hear the results of sea trials this winter.

Marwayne, 

Since you're into such things you might be interested in my use of the water heater for freeze protection:

http://livinlite-owners.com/thread/1477/fresh-water-anti-freezeup-system

Different camper, but might give you some ideas. I also use it to save on FW and Gray water storage when dry camping.

Let me see if I am interpreting the picture correctly.

1. Hot water from the water heater is piped to your new heat exchanger to heat the air.
2. Cool water returning from the heat exchanger goes to the pump and is returned to the cold water line to go back to the water heater.
3. Thermostat controls operation of the pump and fan. Fan can be switched independently to operate if heat is not needed.

With the 179, I added a divider, making a small compartment into which I could install such a heat exchanger and not have it in the exterior storage. That is limited enough as is since it does not go all the way across in the 179. My air return would also have to be different. The remaining questions I have are parts questions. What pump did you use for this? I am going to have to assume it is a 12V pump. What thermostat? For the heat exchanger core, what did you use?

Are the fans thermostatically controlled? 1A draw sounds great for off grid heat. And of course, as always, great work and execution.