My water heater in my 2018 Forest River died a couple months ago, started leaking from the weld on the tank itself. I attribute it to poor maintenance from the previous owners, as I found the anode rod eaten away when I went to inspect it after purchase. Anyways, I looked at tankless, but 1) my input water is very cold in the winter (Tahoe), and 2) I have electric included in my site so I prefer to use electric to power as much as possible. Unfortunately, 120v household plug is just not enough to run tankless. Since I am stationary, and I couldnt find a replacement RV water heater, I ended up buying a small 120v powered 20gallon water heater from Home Depot, placed it under my skirt, and plumbed it to the RV along with an expansion tank. It works wonderfully, and I get way more water and adjustable temperature out of the household heater. I now use my bypass valve as a mixing valve, which gives me even more hot water, by turning up the temperature on the water heater to max but using the mixing valve to cool it with cold water before reaching the faucets.
I am interested in following this though, as I have thoughts of making a portable hot tub with propane heating, and have been thinking of doing this with a transfer pump and a propane tankless water heater.