Keep plugged in or disconnect battery when parked

If they have a single stage converter, the easiest thing is to disconnect. If plugged in, the batteries will need to be checked regularly. They could also plug in to battery maintainers for the coach and chassis batteries which would be really easy. No disconnecting of anything required. The best thing for them would be to change over to a multi stage converter. They are not that expensive and generally not difficult to install. Mine went into the same enclosure as the old converter.