The chassis engine battery is charged by the chassis engine alternator. The chassis engine alternator should be charging the house battery (s) also. You should have 2 separate battery supplies. House battery (s) and a chassis battery.
The onboard coach generator will send 120 volts to the onboard converter charger which then supplies the house with 12 volt power and charges the house battery (s). The converter charger will also receive 120 volts when plugged into a power cord either from your home or a camp site etc.
Keep in mind that the coachman classics of that era had switching that toggled the chassis battery in and out from converter charging and house power usage. Usually a switch in the dash drivers side somewhere.
Its best to get a volt meter and start taking readings so that you are clear what is being charged and when.