For those who inquired...

i road tested the replica of dave garth's hot water heater i recently
constructed.  i went camping over the weekend after about 5 hours on the
road and the system worked flawlessly.  the water in the water tank was
kept at a constant 103 degrees with the fully automatic system.

observations:  i am going to tap the main power supply through the
camper relay so that the thermostat only gets power when the engine is
running.  otherwise, you have to remember to shut the power off when you
are not driving...if you forget....when the water temp drops, the
thermostat will send power to the selonoid, which draws a fair amount of
power.

the water in the tank stays warm for a long time.  i camped in 30 degree
weather...and the water was still luke warm the next morning....it was
not COLD like usual when camping in winter.

the waterbed thermostat only goes up to 103 deggrees.  i want the water
warmer, like 110 to 115 degrees.  i have not figured out how to do this
yet...i was thinking of coating the temp sensor that you insert in the
water tank with silicone, or something so that it would take longer for
the sensor to sese the temp and hence to shut of power to the selonoid.
anyone have any ideas on this?

i am very pleased with the system.  the water did not develop any
strange odors or anything.  this set up will be great for road trips and
for cleaning up the kids.  now i just have to install that shower in the
back.

steve...