Gasoline coaches usually have three batteries. Two for the house part and one for the chassis, to start the engine.
Diesels are different, since diesel engines require a lot more power to crank they usually have two 12volt batteries for the chassis (engine). Then some will have four for the house and two more if it has a residential refrigerator.
I belong to a club that has a bunch of TourMaster coaches and they have three batteries just for the refrigerator, two for the house and two for the chassis.
I believe your coach is a gasoline, so if it was me I think I would want at least two more batteries. One for the chassis, three for the house. That way you could do some dry camping without worrying about the batteries going dead.