I failed to add when discussing the RV500 water heater that I contacted  one of the "satisfied customers" the Precison Webb site contained. It was a Mr. Don Wheat who operations an RV camper store. His recomendation included something about him heating with the RV500. I contact him and he is using the water tank to also provide hot water heater in a trailer.

This is his response to me.
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Roy

I use one heater with a tee off the line to the faucet. There is a check valve on the faucet
line. We use a small March pump for circulating the water. I am pleased with the system and it is much less expensive than other hot water heating systems on the market. It conserves space and uses a lot less power than the conventional forced air furnaces and is quiet.

Give me a call if you would like any further explanation. 360-748-6494

Don Wheat

As I have decided the RV500 is to big a hot water investment for a  trailer that doesn't have a shower and I have not contacted him again. However, the heating aspect seems like a great feature. I once built a house with hot water heat and it was great. So those of you contemplating the RV500 might want to contact Mr. Wheat for further details of his adaptation. It doesn't look difficult but I would be curious what he used for registers and more specifics about line routing etc.

Roy