Just FYI, the Winter 2008 edition of Overland Journal has a great article on building an OBW system. They use the vehicle mounted heat exchanger. I tried to snap a picture from one of the pages but it came out like shit.
What you can't really see if that he has two tanks, and the option for a external input (city water for example), it then goes to a pump, and then a t fitting to allow unfiltered cold water. Then to another t fitting, one side goes to a filter and then out to a tap. The other side of the t goes to the heat exchanger and then out for unfiltered hot water. Its very nice.
But I think, IMO, that for what I would use it for... a portable heater would be fine. I was thinking about the one Sam was talking about and my only concern for it is durability. It seems like its more designed for an RV and not meant to be bounced around in the back of a 4WD. But I do like the fact that you just run a hose to it and presto.. instant shower. I thought that Overland Journal did a review of several portable showers but I can't find the review... and I have every issue. Hmm.. must be going crazy.
I had a couple thoughts on a water source. While a big 25 gallon tank would be cool, its also a lot of weight.. and its big and all in one place. I have 3 5 gallon jerry cans. They have two outputs on them, one as a pressure relief and one for the water to come out. I wonder if a person could use the pressure relief as a air pressurization line, then drop a long "straw" into the other output and have that feed a hose. This could then be fed to anything, a spigot, a water heater.. whatever. Of course a 12volt pump would/could serve the same purpose, I just think you could use the compressed water as almost a pressure washer if need be.
The jerry can top.. the vent fitting comes out, but I didn't want to pull it.
