This is a pretty common thing in marine stores . You might want to weigh the
price of buyin one vs. making one.
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From: Steven X. Schwenk
To: Vanagon
Subject: Hot Water Heater
Date: Sunday, November 09, 1997 11:20PM

    After searching the archives for options for producing hot water on
demand without having to install a gas heater, I have opted to try Dave
Garth's ingenious design.  Back in 1994, Dave routed hot coolant through
a copper coil inserted in the water tank.  He controlled the temp by
controlling the flow of coolant through the water tank with a water bed
thermostat hooked up to a selonoid valve.  He routed the coolant from
the rear heater by taping into the hoses with a Tee.  Dave's design
safely produced 13 gallons of 100 degree water in twenty minutes of
driving.  Dave also installed a shower in the back of his van (ok...a
hand held shower...but with hot water and pressure!...).

Has anyone else tried this?  If so, I am wondering how the setup has
worked over time....
and what type of  plumbing connections i can safely use with hot coolant
(do the joints and connections in the copper tubing have to be
soldered....or could I use the same types of connectors I used when
taping into the propane lines...the flared connections using flare nuts
and a flaring tool and flared fittings...which would be easier?)

Any info would be greatly appreciated.

steve
'90 syncro westy
san francisco