Think about solar...

What charger is used on the 6V batteries? Most RV converters don't push high enough voltage to do them justice.

3 hours isn't long enough to fully charge a pair of 6 volt batteries.

We have 500 watts of solar and this is great when in 5 to 6 hours of full sun.
Do an energy audit; this will determine the battery bank size you need which will in turn tell you the size solar array you need.

Solar is a great thing, however you have some problem in your batteries if two sixes won't last a single night. Batteries lost capacity, lots of load, or inadequate charger for instance.

Have you done an audit of how much power you use each day? We have two group 31s and a 120 watt portable solar panel, and it keeps us fully topped off, every day, for as long as we want to camp (assuming it is sunny!).

But we are just two people, and we use power sparingly. The big hog is the furnace, which we use mostly during shower time. The water pump draws a lot of juice but is only intermittently used. Otherwise, it's just the LED lights and the fridge and the water heater. Those items draw very little power, by comparison.

So my point is that you may be able to get away without a permanent solar panel on the roof. Of course, a roof system has a big advantage -- you don't have to deploy it! But if the RV is in the shade, that is a problem. And the roof panel is flat -- a tilted portable panel is more efficient.