going from 6v to 12v will reduce the life of the batteries as 12v batteries do not deal with the discharge/charge cycle as well
Just for the record, that has nothing to do with 6v vs 12v - it is a matter of battery design. If you buy a quality deep cycle 12v, e.g. a Trojan or Lifeline, they will last every bit as long as a GC2 (golf cart) 6v. And if you found a 6v starting battery (they are still a few made for vintage cars and such), you would find they don't last very long either.
However it is true that the 12v batteries sold by most battery or RV dealers is often designed as a starting battery, or at best a combination start and deep cycle (often called a "marine battery"), and not the best choice for a long life in RV use.
2004 American Tradition; 2014 Buick LaCRosse
Homebase in the Ocala Nat'l Forest near Ocala, FL