Propane water heater
I read about a chap who changed his Lesharo to a heat exchanger. He runs the engine, which flows through the exchanger, heating the water as it is used.
It is "on demand", no wastefull storage, but the engine must run while hot water is being drawn.
I ran across a 30 Plate Brazed Heat Exchanger for about $100 shipped(from dudadiesel on Ebay). This is a food quality heat exchanger unit, so there is no cross contamination between the heat source and the fresh water. Best thing is the heat exchanger is rippled so turbulence is forced into the heat exchanger, making a more efficient heat transfer. I set a unit up using my home hot water heater of a "hot" source, and the rv fresh water pump for the output source.
The results really impressed me, as the water heater was set to 115 degrees, and the temp of the water came out around 110 degrees! So on to the next stage.
I reestablished the coolant lines on the LS and install the exchanger as shown in the photos below. I ran the engine for around 5 minutes, to bring it up to operating temperature, and turned on the tap. I could make tea with the water! The tap temperature was around 150 degrees! I later took a short 10 mile drive and had steam come out of the tap! This was the answer I was looking for. I installed an inline ball valve to turn off the coolant supply while driving, to prevent the fresh water side from boiling and blowing a line. It takes about 5 seconds to heat up the exchanger once the valve is opened.