Would this be in addition to the regular tank water heater? I wouldn't want to give up the propane option when unplugged. We had tankless in the house. It was quirky sometimes. Sometimes it would just suddenly stop. However, it may have been because it was aging. When it died we replaced it with a regular tank, mostly because of the huge replacement cost.
I don't know how long you have been RVing. Do you have a shower wand that you can turn the water on and off to save water and make the hot water last. With a hook up you have unlimited water which is great but you still must conserve the hot stuff with the small tanks water heaters have.
One of the great pleasures is coming home or getting to a hotel and taking a LONG LEISURELY HOT shower.