Below is pic of my battery box with two 6V batteries. I welded up a hold down and proprietary hardware for two hockey puck style locks. The opposite side is identical.
Two 6V batteries are far superior for dry camping to two 12V batteries. There is NO 12V battery that is a true deep cycle, tho they aren't shy about calling them that. Golf cart batteries can be cycled thousands of times. 12V batteries, not so much. And you can safely cycle SOC lower with golf cart batteries than you can 12V batteries. There is a reason that 6V batteries (not 12V) are ALWAYS used in golf carts, and for industrial uses.
The alleged risk of one of the two 6V batteries failing is infinitesimal. When these fail, it is from finally wearing out, so one begins to notice that it is time to replace them and is not left stranded.
free upload image