Thanks again all.  This is great info so I appreciate the conversation!
I am pretty sold on 6V at this point as we do plan to boondocks more this spring / summer /fall than we ever have.  I did more on-line digging and found the Sams club Duracell's at $89.  Of course the nearest Sam's club is an hour away.  Costco is our regular bulk warehouse at 10 min away and as stated mine has stopped stocking the Interstate.  My in-laws have a Sams near them and a membership (again an hour from our house) so we will give it a shot next time we are down that way.  Next challenge will be to find battery boxes that fit.  Looks like a few nice ones on Amazon.
Thanks again all!