If all you want to do is charge the house batteries while driving, you don't need a converter at all. The converter converts 120v AC from shore power to 12v DC that you can use to power 12 volt devices or charge the house batteries.
The simplest way to charge your house batteries while driving is to connect them directly to the alternator. The problem with this setup is that when you're camping your starting battery will run down along with the house batteries. To avoid discharging the starting battery you can use a manual disconnect switch (which relies on you remembering to disconnect the house and starting batteries) or as GB said, install a solid state battery isolater or an ignition switch activated solenoid. Both will automatically break the connection between the house and starting batteries while the engine is off and also allow the alternator to charge both while driving.
RV electricity has a pretty steep learning curve.