Water heater shut-off valve

We rustic camp quite a bit.  In our last campsite water was particularly hard to draw from the well.  

In my 1999 2720 the water heater must first prime with 3 gallons of water before water pressure can be had.  This is 3 gallons of unusable water.  If I would put a shut-off valve on the inlet side of the heater then I could use cold water without having to first fill  the water heater.  

[I could also keeo the water heater filled but I like to tow completely dry.]

Has anyone done this; where can I get the fittings for the  plumbing tubing that TM uses?

[mjlaupp]

What you need is a water heater bypass kit. Have seen them at my local RV dealers and online at RV supply centers
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