Bought a Jayco 29MV recently and the first mod was water heater replacement. We were camping in 30 degree weather and the tankless was totally unusable. I was schooled in the proper operation which said to use hot water only and adjust temp by the flame controller. Ended up wasting a lot of water attempting to get the temperature right and then it wouldn't stay. Tried to modulate the temp with by adding a bit of cold and the water heater would shut off from low flow. Arrrggggg! It was a real exercise in frustration.
The last two MHs I've owned have had regular water heaters and worked very good. AND we could use the energy provided by the campground instead of using our propane.