Thor had a recall about 5 years ago on several coach series, of various years, related to the RV Custom products BCC where the chassis battery latching relay could fail open, cutting off the chassis battery and basically stopping the engine if it was running. So that means “dead in the water” while driving or at night potentially. The recall basically moves the cable from the Chassis Switched post to the Chassis Battery post on the BCC.......but first requiring that the coach disconnect switch is turned off and the chassis battery + cable is removed at the battery.........for safety reasons. They basically are hard wiring the chassis ignition feed directly to the chassis battery. You still require a working chassis disconnect latching relay though for the various other loads it powers......like steps etc. You should be able to do a Google recall search on Thor for this issue and a formal recall instruction document (or call Thor).
RV.Net Open Roads Forum: Class A Motorhomes: Thor Battery Control Center Recall
Just a side note, if you are operating the coach and chassis disconnect switches near your entrance door and you do not hear the appropriate latching relays functioning to close or release then you need to check the relays........sounds like you found out how messy that is already. You should also see the lights on the switches when they are on (and you are not on shore AC). I am surprised you said your latching relays were OK since you still had this starting problem.