its anybodies guess as to how the battery systems were actually installed, or what kind of devices it has...
is there a battery shut off switch on both the coach and the house batteries? does it have a battery "combiner" switch?
does the coach have a security or anti-theft system installed?
are there any aftermarket components that may have been wired into the wrong circuit?
or compartment lights or step light that may be staying on?....
there are many reasons for a battery drain and its usually something simple that someone has overlooked....