The reason the generator ran with the old battery hooked up is, when the generator is running the converter is supplying 12 volts to the coach and the dead battery. With that battery disconnected you need to have the POS cable isolated or you're going to cause yourself more problems if it touches ground. If you are going to run anything without that battery.
Your coach may not have a disconnect switch, my 95 Challenger did NOT, but it had an automatic transfer switch. Yours must have one too if you didn't plug the cord in anywhere.
My 95 Challenger also didn't have a BCC, instead it had 2 isolation solenoids, one controlled by the emergency start switch and one controlled by the ignition switch in the run position. It charged the house batteries from the ALT but didn't charge the chassis battery when plugged it.
1996 Challenger 313
2003 Dolphin 5320 sold