Interesting item on ebay:
http://snipurl.com/fbvb

Never seen anything like this before.  Only 16" tall and 7" in
diameter.  I'm not sure what I would use it for in my vanagon
though.  Maybe to heat up a significant quantity of water for
bathing?  Mount it outside, plumb it into the rear heater core and use it
to heat the interior?  That idea doesn't sound very efficient.  I wonder
how it regulates the propane so as not to just flash the water into steam
if you stop pumping?

Edward