I am not concerned about wiring 2 new 6 volt golf cart batteries in series from a reliability point of view. The odds of one battery failing (in one of the three cells) is no different than one cell of a
12v battery which would also shut you down. I am told that all the boat people are doing this because the 6 volt Trojen golf cart batteries are so rugged and offer better value for the money. Going with the series/parallel idea with 4 batteries doubles the capacity and, if needed, seems like a good idea. I have not gone the inverter route for 110v just because of the cost. (I do however have a cheap 600wt inverter for small thinks like shavers etc,) I agree, keep things simple