For what it's worth, I am a big fan of the American made Precision Temp Products and their all American customer service is second to none.
When I did our renovation I installed the Twin Temp JR. which does awesome coach heating and instant continuous hot water as well. Hands down the best thing we did on the renovation and probably the single most expensive$
Precision Temp has the RV-550 that does just hot water, two models one vents though the floor and one uses the side access panel.
We boon dock often and it works great on 12v
and propane. It does have a 110 switch for when you are on shore power. Saves on propane.
Bold, it works great with the 12v
water pump when boony camping.
The space and weight saving is great. Plus it's nice having as much hot water as you want, all the time if you want it, and the wife loves it.
Compare the efficiency, outputs and service before you choose. A little more $ now could save you $$ and headaches down the road.