I have not owned a tank heater in almost 20 years…in my home. Since I installed both of my homes tankless units and I can only say its truly a DIY job and you will be glad you did, great $$$ savings, all the hot water you can use.
But alas it seems the tankless units in RV’s are problematic at best. IMO that is because they are RV grade units, meaning cheaply made, poorly made and designed.
You should at a PoU (Point of Use) model that are common in Europe and Asia. These have been around for over 50 years and work very well.
That said electric ones are not as efficient and use a lot of juice to heat water on demand, not RV friendly IMO. The 6/10 gal DSI units are still your best bet for an RV IMO.
US Army Retired
2019 F 350 CC-LB King Ranch
Hill Country of Texas