To answer the original poster's question, a solar panel mounted horizontally on an RV roof, and not shaded by the air-conditioner, etc., puts out in daily amp-hours about 1/4 of its wattage rating around the summer solstice, and about 2/3 of that around the spring and fall equinoxes. This is a rule of thumb that has developed over the years and verified by many RVer's who measure battery input/output with an amp-hour meter. Charging is only about 90% efficient, so multiply your daily panel output by 0.9 to find your "usable" amp-hours.
Before you decide how much of that you can use, you have to subtract that used by your RV, for the LP detector, the circuit boards in the appliances like the refrigerator and water heater, and the radio remembering its station settings. One way to find this is to turn everything off in the trailer, remove the negative lead from both batteries, then using a multimeter than can measure DC current between one of the negative leads and the negative post on its battery. Multiply that times 24 hours to get daily amp-hours.
Many RV appliances today have electric solenoids that control the propane flow. While the multimeter is still connected, turn on the refrigerator on gas and the water heater, one at a time, and record any increase in current. This you will multiply by 24 hours and again mulitply by the duty-cycle, the percent of time the solenoid is "on." That's hard to estimate and one of the best reasons for using an amp-hour meter.
You can also turn one light or other appliance on, and note its current draw over the base amount. Just don't exceed the rating of your meter. The one appliance that will probably draw the most power would be your furnance, and on larger RVs its fan can exceed the rating of a 10A meter. So can smaller furnaces during fan start-up. One worth checking is the Fantastic Vent fan since using solar means you park in the sun.
You may be surprised, especially with a larger RV, just how much electric power you use.