Hi,
The water heater would use about 8,800 Btu's per hour, or about 2 KW per day to replace just one hour of propane run time.
The refrigerator can be replaced with a high efficiency electric refrigerator, and then install a pure sign wave inverter to handle the high torque of the compressor, and you can save running that load on propane. Yet even that load is only about 10 gallons of propane in around 6 weeks of camping. I used to fill with about 15 gallons of propane every 6 - 7 weeks while full time in the RV, and mainly using just the refrigerator and water heater in the summertime. Winter I would use a lot more propane to heat the RV, depending on where I was located.
I have a 415 rated watt solar system, and it charged the batteries only. I did not use the inverter to power the refrigerator or water heater.
Fred.