PT, I like HiTech's suggestion of using your engine as a generator. I'd swap out your alternator for one of those marine units with a 3 stage regulator. At least a 300 amp unit. Something that will actually not******out running as a charger. Upgrade your wiring from the alternator to the batteries to 4/0 if the distance is relatively short or double up the wiring if it's long. I'd get that Victron 5kVA inverter so you can run two 1500W heaters and charge your batteries at the same time. Or if that's too much money, get two 3000W Go Power inverters and dedicate one to the heaters and the other to the coach. You might need MEX's help in getting the right alternator that can handle this kind of load at idle.