Something else to consider. Most RV's don't charge the engine battery even when on shore power. And there usually are parasitic drains. These are powered items that are always on even when the ignition key is off. Some may be connected to the house battery and others to the engine battery. Fire and security alarms, radios (w/ clocks), are some examples.
So you need to use a battery maintainer on your house battery also.
This is rare, but some new vehicles may have a built-in system to charge the engine battery too, so check with the manufacturer.