It's coming soon - hot water recirculating system.

Coming this spring, I intend to do a full hot water recirculating on demand system with temperature limiting control (since the water heater is set to 140). I am a licensed master plumber who hates to see water wasted down to the grey tank and out of the fresh tank waiting for hot water to reach the faucet all the way to the back of my 179. The recirculating system will be less than $100 and be fully automatic at the push of a button with no permanent modifications to the camper. The temperature control will cost about the same and will require modification.
I'm in the process of engineering it now and am looking for advice from others who have already done such a thing.
After I make it I intend to do a full instructional post with pictures.
I know you CAN catch the cold water in a pan and use it for tea/coffee. But, I must tinker.

Forgot to mention my system will be run on 12 volt not house power like most of the systems are made for. I don't always have hookups and that is when it is even more important not to waste any of the precious 36 gallons.

Using the above idea with a loop under the mattress would make a heated bed.

   Lance campers for their model 1575 have a instant propane hot water heater and you are able to dial the temperature you desire at the time you need hot water. I don't how well it has worked out but sounds like a good idea. Forget the manufacture of hot water heater.    ( I have looked back at reviews and the tankless hot water heater has not been well liked by owners. I went to the Lance manufacture website and there was no mention of them, my guess they have been discontinued with the Lance 1575.)

Fred, interesting device.  Doesn't sound like it has a pump or thermostat.  You probably could go cheaper with a $50 transmission cooler and $5 computer fan.  Add a 12 volt thermostat, relay, pump and you would be golden.