Be sure to search this Forum for `tankless' before deciding on what to do. IMHO I would never have a tankless in my RV unless it is at a site with full hookups. I think the rap against them is that one has to have the water on full blast for awhile to get the water up to temperature and keep it there for the duration of the shower. No shower stages eg. rinse, stop, lather up, stop, wash hair, stop, rinse again.
Maybe someone who has one can tell you how great they are.
Dick_B
2003 SunnyBrook 27FKS
2011 3/4 T Chevrolet Suburban
Equal-i-zer Hitch
One wife, two electric bikes (both Currie Tech Path+ models)