If you can't regularly start the genset to top up things, you'll need to at least disconnect the battery cables altogether - even with main switches off there can be minor parasitic drains that would add up over 9 months. It would then be preferable to remove them to somewhere that they can have Battery Minders attached and kept optimized.
If that's not practical, then when you do return be prepared with a portable device or long jumper cables, which may be needed to start the genset; then let it run until the inverter panel reads at least Absorb Charge, a safe state of charge that won't stress your alternator when you subsequently start the engine. Using jumper cables for the genset start may not be so easy depending on how the coach is parked and your ability to get another vehicle oriented alongside, so keep that in mind.
Joel