For people who have campers who are looking for hot water, I've seen
a hot water heater (that is, it only _heats_ the water, it doesn't have
a hot water tank) for motor home applications.  It's pretty small, and
needs to be vented outside (since it runs on propane).  Basically
the water runs into the box, and comes out hot.  I don't remember 
what the output was (15-20 gals/hour?), but it seemed to be a reasonable
volume for showering.  Those who are used to 30-40 gallon showers will
probably be disappointed by the performance, though.

The water heater is about the size of a catalytic heater, runs on 
propane, and I believe was $495.

Oh, and it's made by Bosch.

-Jim Macklow
macklow@sybase.com