As stated, wire (2) 12v batteries in parallel, using battery cable (short sections available at auto parts store). If there is 120v power available, just plug your RV in and the batteries will charge (assuming you have a working converter / charger or inverter / charger).
If you want to use an external charger, connect the charger to the positive post of one battery, and negative on the other. Your 6 amp charger will take a while to charge a 230 ah battery bank... I use a 40 amp charger occasionally on mine.
Solar is connected to the batteries the same way at the battery, but you will need a charge controller between the panel and battery. I do not have solar, so I have no more specific suggestions.