Most Class C will also charge from the alternator.
What I did 3 years ago was buy a battery tender
that had a plug on the end that went into the
dash power outlet.
It has kept my 2 coach batteries and the starter battery
(Parasitic Draw is always a problem) charged and ready,
without problems.
http://www.flashoffroad.com/electrical/Batteries/BatteryDrain.html
A good diagram of RV electrical:
http://www.metrotrekkers.org/utility/electrical.htm
You should have a battery disconnect as in the diagram above.
If you are only concerned about the coach batteries you
should be able to disconnect them from the circuit.
Use the interactive functions in the diagram to see how the
system works at various times.
Hope this helps.