I recommend AGAINST optima, because you get only about 60% of the capacity of the same footprint (Size) Lifeline or Deka AGM. Though Optimas have their place, for example when you are slamming over ruts and rocks and logs on your 4-wheeler,, Optima is the only choice, any other battery will be beaten senless. (Just like your kidneys) but for RV use, no way.
I'd go with six volt golf car batteries, one or two pair
one pair of six volt, in series Well let me put it this way
What you ahd
-{Battery}+
-{Battery}+
What you get with 2 pair of sixes...
-{BAT}t{ERY}+
-{BAT}t{ERY}+
The lower case "T" is the jumper wire of course.
And you might notice teh BATtERY is much bigger in the second example. IN fact one pair exceedes a pair of Group 29's (But not a pair of Group 31s).