A friend of mine has been tossing around a few ideas for designing an on demand water heater that wont require bringing along a propane tank or a serious power inverter. Before he puts too much time and effort into trying his ideas he asked me to see how much interest there was for this kind of thing.
The basic concept is to have a water tank in the vehicle with a pump and using heat from the engine (he has a few different ideas on how best to do this) to provide hot water. He is going to do his best to make a universal kit.
If you have questions or ideas, I will pass them to him and get answers as quickly as i can.