FG, FYI,
In most cases, a motorhome has a relay that can join the coach and chassis battery with a press-and-hold switch allowing both sets of batteries to be used to start the engine or generator. This same relay is often automatically closed to connect both sets while charging them. It also disconnects the chassis battery if total system battery drops below 12.7V (to ensure the chassis battery can still start the engine). Additionally, while driving and producing current from the engine driven alternator, the coach batteries are automatically joined to the chassis battery to charge the coach batteries from the alternator.
He will have no need of jumper cables if his motorhome's BIRD and solenoid are operating correctly. Even if they aren't, they are on a common ground, and the two (+) can be joined with a single jumper cable clamp spanning both contacts.