Always have two batteries. It is utter nonsense that Thor would be so cheap as to just install one. As noted two golf cart {6 volt}, batteries are a good choice "if" you have enough room. They are taller and often you will not have enough clearance for the batteries and if they fit there is no room to check/fill them as needed.
Two 12 volt batteries is what most folks have and they work well and can be replaced just about anywhere {replaced my two GP 27's with new Interstates from Batteries + for $100 a piece}. Most RV's don't need a lot of DC power, lights and the water pump draw very little. Slides and the furnace fan {the largest draw in any rig}, can both suck down your available capacity.
Having just one battery is simply a problem waiting to happen, think when - not if.
:C