2 Camper Batteries 12V or 6V

I got to admit this is interesting on howmany go with 6V batteries. I have found that they do last longer for some reason. I have done some research on that and I should atleast get longer life out of them. I have done the math and I the AH is longer with 2-12v but I have a buddy who had 1 of his 12v die on him after 2 years so then replaced them with 2-6v and he said it seems they do last longer than his 12v did. The cost for the 2-6v batteries for me was only $40 more so it wasnt a huge deal for me but I do Dry Camp alot of the time! So I do worry about how long they will last I plan on trying them out in a week for a weekend and see how low they get!
Check this site out- http://www.pbase.com/mainecruising/deep_cycle_battery

Thanks for everyone comments! I think this forum is great I just signed up but I have read posts on it for the last couple years!