I'm a newbie here and just to keep this thread active....
Most of my boondocking/dry camping is 7-15 days of fishing in the early spring or hunting in the late fall. It is usually 40-60 miles to the nearest town, temps to 15*F at night and there is always the threat of snow. Therefore, I would never, ever think of using sets of 2 volt or 6 volt batteries in my TT because of 1 simple fact. Batteries die.
If 1 of a set of 2 volters dies, I can not sustain the TT. If 1 of a pair of 6 volters dies, I can not sustain the TT. If the truck battery dies, I can start it but it will not get me to town unless I take 12 volts worth of TT batteries with it. So, I match the size of my TT batteries to the size in the TV and mix/match if needed. Of course, your mileage may very.