I will be curious what you find. If the heat exchanger is aluminum, you will likely need a coolant loop, as raw water will corrode the aluminum. Though you could have the unit anodized to make it resistant enough to corrosion for using raw water.
Need to heat up the van on those chilly mornings, better yet want a solid option to heat water for warm showers that won't deplete my battery off the inverter.
I just installed a chinese 10A 12V regulator from amazon in the rear pillar for the maxxfan and lighter sockets which power the dometic cooler. What would be a good product to step up 12v-24v for this heater application?