There are a few companies in Australia that are making them. I've considered that myself, but ended up going with a 12v pump, water tank and then a Camplux portable shower system for heated water. Just use ambient temp water for cooking, washing dishes, etc.Years ago I bought a heat exchanger, a copper tube with another copper tube inside it so it is a heat exchanger. Has inlet of one end and outlet on the other. You put a hose into a bucket of water, stream, etc., and pump sucked up water with a 12 volt pump through it and out into a shower hose and spray down. Uses the dash heater settings for warmer or colder. The company that made it was in CA but is now out of business.
Easy, versatile, always there.
Does anyone know of a company that makes such a device today?