Teardrops n Tiny Travel Trailers

For my needs I was planning on demand water heater outside of trailer with 12v pump to supply water to unit.
My concern is how do i know how to set for proper temp of water inside in the shower while the unit is outside.
I want to keep the unit outside so I dont have to deal with venting through the trailer wall.
There will be no mixing of cold water for the shower just straight showering from the heater itself.
Maybe someone who has one can shed some light. Thanks

I did exactly this on my truck camper. I mounted the shower outside the back wall. I added in a remote toggle switch which allowed me to turn the actual burner on or off, so if I only wanted cold water, then the burner was off. As to setting the temp, it was pretty close in most cases without much fiddling. The temperature rise is the same in degrees from the input temp. So, rise of say 50 F on medium setting, input temp at 75 = output of 125, input @ 50 = output at 100F. Low setting , rise might be only 30 degrees and high setting maybe 70. I put 3 markings on the twist knob to let me know what the expected rise would be and adjusted to there.

I made an adapter to be able to use either the "D" cell batteries or plug in to the camper's 12 volt system. The switch controlled from either.

BUT, if I wanted to upset my wife, who had just spent an hour waiting in a line at a public shower at a full COE campground in Texat for a crappy shower, I took my shower in the camper and would ask her to adjust the water temp a bit, because it was slightly too cold...oh, I meant too warm....nope, just a tad too cold. Then she shut down the burner on me to get even. :-)

dave

So if I am understanding it correctly, if i were to know the input water temp and the final temp i wanted i could determine the rise i need and have some preset marks that actually are telling the amount of temperature rise i get in the water (aproximate).
Basically treat the dial as an amount of temperature rise knob.