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.
2002 Gulf Stream Scenic Cruiser
330 HP Caterpillar 3126-E
3000 Allison Transmission
Neway Freightliner chassis
2017 Buick Envision