I hope to do something very similar to my Seneca for the same reason, to conserve water when dry camping. I have a TS, so I am certain the plumbing layout is different. But similar to SloPoke's FK my kitchen sink is also the furthest fixture from the water heater, so that is where I will likely tie in too. I already swapped out my unreliable Girard tankless for a 10-gallon Atwood XT gas/electric water heater, so consistent hot water is always there just waiting. This mod will bring it to the sink, but the shower also benefits since it branches off before the kitchen sink.
One addition I am researching is a timer circuit that will hold the solenoid open for a pre-determined (and hopefully adjustable) period of time. It's not that holding the momentary switch is that difficult, but the DW would better appreciate being able to just press a button and then climb in the shower knowing hot water will be there in 3 seconds instead of 30!
Thanks SloPoke for providing more motivation to get this done!
2014 Seneca 37TS
Toads: 2014 Ford Explorer Sport or 2013 Ford Focus ST