In RV park. Now have car to drive. Disconnect RV battery?

You did not describe what your RV is, or where you are parking it. If you have shore power available, you should be able to plug in your RV shore power input cable and that will keep your coach batteries up. Most RVs do NOT charge the engine start battery from the coach battery charger, but assuming there are no parasitic loads on the start battery when parked, it should not discharge after a month or so.... but still, you might consider a trickle charger for that battery if sitting for longer periods.