FWIW - as in generic information is usually better than none. ;-)
There is usually a disconnect for the "House" batteries and may be one added for the "engine" or "chassis" battery. Follow the heavy wires looking for a switch or heavy duty relay.
The step area is a common place to put the switch for the house disconnect. That would indicate the one by the steps is probably what you want.
There is also often a way to connect the two battery banks together to start the MH if there is a problem. It makes a lot of sense to keep the systems separate and to understand how each battery set is charged. They use different battery types as well. Lead technology but different internal designs to accommodate different load types.
You might find this interesting:
The 12volt Side of Life (Part 1)