Steve-
I can't speak to the camera issue, but as to a safety issue whenever I deal with battery connections on any chassis-grounded configuration, my rule of thumb is remove the grounded cable first and put it back last. You said you disconnected the positive cables first.
As long as the battery is connected to the chassis, it leaves open the chance of accidentally short circuiting with a tool from positive post to surrounding chassis metal - it's essentially equal to laying a crescent wrench between the two posts. With the ground disconnected, electrons have no pathway back to the negative side if your wrench or a screwdriver handle touches anything while working the positive cable.
Even with switches and solar off, there can still be something on line, such as drivetrain ECM's, that isn't subject to the switches. So there can still be a slight arcing, but I'd expect it most likely with the chassis batteries. It sounds like you covered all the bases prior to, so I'm not sure what would be bypassing the coach main switch to the battery bank unless it's some aftermarket add-on. Is the camera routed properly through a circuit breaker and terminal buss in the electrical bay?
Joel