If two N27s served him well before, why change. I wouldn't.
One disadvantage of using two six volt batteries is that if one fails, you no longer have any 12v power from your batteries. If you have two 12v batteries and one fails, you still have a 12v power supply with one battery.
Another advantage of a dual purpose 12V batteries is if you are boon docking and your TV battery craps out, you can take a 12v batter from you RV and put it in your TV.
Granted, dual purpose 12v batteries do not give you the long lasting power supply that two truly deep cycle 6V batteries will, but they give you more flexibility to improvise.
As always, I say "to each their own". What ever works BEST FOR YOU!