Since you seem to have a metal carport I would go with a standard solar panel in the 100-130 watt range, with charge controller, etc. As this would provide enough power to let you run an exhaust fan on low and keep interior humidity under better control. Best if you have a temperature controlled fan.
Which should be turn key for your situation minus the mounting screws, though you might have to add some more cable, the included dual ended 30 ft MC4 cable is intended to be cut in half to reach between the solar panel MC4 plugs and charge controller screw terminals giving you only about 15 ft of range from the panel to the charge controller.
A cheaper smaller panel option would be https://www.ebay.com/itm/Newpowa-30W...m/121465172147
which would probably be enough to maintain the batteries, but would require you turn off all electrical items. (fans, refrigerator, etc.)
In my personal opinion in much of the US anything under about 30 watts of solar on an RV with 3-4 batteries will just slow the discharge, not maintain the batteries.
Also if you don't have one or something similar consider getting a Ultra TRIK-L-START Starting Battery Charger/Maintainer
to maintain your starting battery as well as the house batteries.
p.s a Fantastic-Fan or MaxxFan draw about 1 amp when running on the lowest speed http://www.wanderthewest.com/forum/t...ing-amp-usage/
Running 24 hours per day this is about 288 watts per day, on an average north america cloud free day a Solar panel at optimal tilt angle with no obstructions will generate about 6 times its rating in watts per day (so a 100 watt panel will give you about 600 watts per day in optimal situations). A shallow southern facing tilt will give you about 4-5 times its rating per day, so you can see that a 100 watt panel on less than optimal tilt does not give much excess running an exhaust fan on low, once you add in charging losses, etc. All bets are off if you live in a cloudy region.