If your goal is to fully recharge your batteries with solar power, you need to know how much power you typically consume in a 24 hour period. The best way to do that is with a good battery monitor, as Gary mentioned. The Trimetric RV 2030 and the Victron are probably the most common, and both get good reviews from RVers.
Make sure your batteries are fully charged, then camp somewhere for 24 hours (even in your driveway.) Do everything you would normally do - watch TV, turn on lights, charge your phones/tablets etc. After 24 hours, look at the battery monitor and see how far your batteries have discharged - in percentage. Both the Trimetric and Victron will display that information.
Look at your batteries to determine their amp hour capacity, or look them up online. Let's say your batteries (combined) have a total AH capacity of 240 AH, and after 24 hours, your battery monitor is indicating 50%. That means you've consumed 120 amps in 24 hours. That's how many amps your solar panels are going to have to generate to fully recharge your batteries.
A single 100 watt solar panel will generate about 7.5 amps per hour under ideal conditions (which rarely exists.) Most experienced solar users will build in a "fudge-factor" to help compensate for cloudy days and installation inefficiencies. Depending on what part of the country you're in, the solar charging window is about 5 hours per day in the winter (when RV solar is usually more relied upon) and roughly 8 hours in the summer. The average cloud cover in different regions will also have a significant impact on how much charging you can expect to get out of your panels. Keeping your panels tilted toward the sun will also have a significant impact on how much power they generate - especially in the winter.
So to best ensure that you get what you want out of your solar setup, there are some things you have to know first. On the other hand, a lot of folks just slap some solar panels on their RV's roof and hope for the best. Good luck, and let us know if we can help.
Kev