The bigger the battery bank the better. Unfortunately most RVs have very little ventilated space for batteries. You are lucky if you have room for 2 X 6V, 2 X grp 24 12V or a single 4D battery.
Getting around this problem involves getting into the marine world a little & changing to non venting batteries. In cruising boats it is very common to find batteries right underneath berths. What makes them safe is that they are non venting sealed AGM or Gel type batteries. These types can be put anywhere there is space in your unit. The limiting factor, besides weight, is cable length & VD.
