Been down the 2x6V or 12v route. Several years ago I bought 6V golf cart batteries - big mistake..... They were expensive and they only
lasted a couple of years. Now I buy 12V Marine batteries from from Walmart (~$90) each.
I use 2 12V batteries and have been using a Quiet generator to top them up. This year I bought a 150W Solar panel (with controller) and I tested it a couple of weekends ago.
I'm sold..... even during overcast days, the batteries were being topped up. I'm going for a 6 day "dry-camping" spell and will only take the Solar panel.
Gerry