If the battery disconnect is off and the batteries are still being drained, something is still connected or the disconnect is faulty. First of all, put a battery charger on the batteries and make sure they are fully charged. Now, I would start by testing the battery disconnect. Disconnect from shore power and/or generator, turn off the battery disconnect and check for 12 volts after it. If new batteries are being drained and the disconnect is off I would make sure that there are no other connections between the batteries and the chassis. On my Seneca, it has electric steps but when I turn off the battery disconnect, the steps don't retract until I close the door so there is still a separate connection to the steps. With the battery disconnect off, I would check any 12 volt connections that I could find and see if any still have voltage. If you find any voltage I would go to my DC panel and pull all the fuses, (take a picture first for reference) and check back at the connection where you found the voltage. If the voltage is gone, slowly put the fuses back in until the voltage returns and try to trace that circuit. If the battery disconnect is off and the batteries are still being drained, something is still connected or the disconnect is faulty.
Maybe someone who has had a similar problem will chime in.
08 Seneca 36 MS
2002 Chrysler PT Cruiser-TOAD
1975 Triumph TR6-in progress
"For evil to triumph, good people need do Nothing!"