Walt,
The ECM (engine control module) for the C12 on your coach is wired to the chassis batteries before the cutoff switch, and it has nearly a 2 amp constant draw for the keep alive memory. To solve this problem, the coach needs a charging source (either solar or shore power) or a heavy duty marine style disconnect directly at the chassis batteries.
If the batteries are disconnected from the ECM, the keep alive memory is lost, but it will be rewritten in about a minute after power is restored.
Gerald