Re: buying a battery
As a career electrical type, I suspect that your one battery will do just fine since you don't plan to stop where there are no hook-ups for more than a quick meal. Batteries do fail eventually, even if you don't use them so to buy more than needed is just wasting money. Your new battery will last far longer if you keep a float charger of some type on it. There are several good ones and you can get one at Wal-Mart. Lightly used batteries gain more from the float chargers than do heavily used ones. You do need to check for proper electrolyte levels in your battery at least twice a year and adjust to proper levels using distilled water. If it is kept charged it should last for a long time.
If you think that you will spend the night where there are no power connections and wish to use the furnace or any of the larger electrical loads, they I would put in two batteries, with two 6V, connected in series being the best choice in my experience.
