There are many conflicting opinions on this exact issue -- do a search on rv.net and your head will spin. So this is just my opinion, after doing lots of camping for the past ten years:
I have chosen to go with two 12 volt flooded batteries. They are group 31 from Napa -- 110 amp/hours each, weighing about 59 pounds (the most I can lift, safely). I use one and keep the other one in reserve. I use each battery till its voltage drops to 12.1, usually after three days of camping, and then switch to the other one.
Here is why I favor 12 volt flooded --they are cheap. Batteries need to be replaced every few years, and these are about 150 bucks each, which is a lot less than 6 volts.
And the reason I use one and keep one in reserve is safety -- if one dies, I have the other one ready. If you hook up two batteries together, and one dies, the other one gets drained quickly, and then you have nothing.
There are good arguments against my way of doing it. First, hooking two batteries together means less total draw, due to something called the Peukert effect. I can't explain it well, but you can look it up easily. So I am losing that benefit by not hooking them together.
Second, people think that the six volt batteries are more robust and will last longer. Probably true. But does the long life justify the cost?
If you have solar, that may change things, because you can recharge almost every day. I don't, so I need batteries that will do the job without recharging. Once I remove a used-up battery, I sometimes run my generator to recharge it.
Whatever you do, don't over-discharge the battery -- it will really shorten its life. And when you get home, immediately recharge. Then put the batteries on a Batteryminder Plus or something like it -- it will prevent the plates from getting covered in sulfur crystals.
Be sure to get opinions from other folks -- this is just my own viewpoint, and it is a pretty basic and unsophisticated approach.
