We have two group 31 batteries -- one that we use, and one as a spare. (Real battery experts will tell you, correctly, that you will get more battery life if you hook them both up at once -- a thing called the Peukert effect.) But I prefer to have one as an actual spare, so that if the first one quits, it will not drain the spare. I am a very risk-averse person, so you have to take that into account when evaluating my comments.
Anyway, we do a lot of boondocking and dry camping -- check out the links in my signature below. We can go for three nights on one battery without recharging it (see below) until it is time to swap it for the spare. (Never let your battery get below 12.1 volts, is what they say.) And we can go four or five nights before the gray tank needs dumping, so that is a limiting factor.
We also have a Honda 2000, which I almost never use (except running it monthly at home for maintenance). I go camping to get away from the noise of the city, not to bring it with me. We have a 120 volt portable solar panel, which feels like having the ability to mint money from thin air -- it fully tops off our battery every day, and lately we are not swapping out the spare. (And yes, I rotate the batteries -- on one trip, Battery A is the spare, and on the next one, Battery B.)
Approximately where on the west coast are you located? The camping out west is just amazing -- good weather, lots of room, lots of variety.