I've been using tankles for 50 years (they were/are pretty popular in Europe) and have mixed feelings about them.
Great thing in household application is small space and options of easy installation of 2 or 3 in the house, so you don't have to wait for warm water to come. That doesn't apply in RV
When you are buying one, buy the biggest flow you can as it will always be "not enough".
Bare in mind that tankless has limited temperature raise so when it is giving you 5 gal/minute raising from 70 to 100, it will be 2.5 gal/minute starting at 34F
