I use the Zodi Traveler water heater whilst camping.  It works really well,
except for the built in igniter.  At Burning Man, I made the mistake of
letting the water re-circulate for a few minutes before showering, man it
was hot!  I had to add a gallon of cold water before showering just make it
bearable.

I got mine directly from Zodi through eBay.  IIRC, I only paid $60 for a
factory blem.

Cheers,

Jeff