I installed an on demand water heater
in my Winnebago (propane) and I'm not thrilled with it. I suspect water pressure is the issue and I need to up the pressure to improve performance. You will read about cold spots with some and mine has that in spades. And the heat seems to come and go, either the water isn't hot enough, or I'm scalding my hand, and which point, it goes back to tepid.
When you find one that you feel is suitable, review, review, review it, before purchase
I do have a home on demand water heater - natural gas - which I quite like
I'm trying to remember which brand I have but recall
is evading me.