The salesman switch or battery disconnect switch should be located near the door. It operates a latching solenoid which if off would have your symptoms. This part has 2 larger wires and 2 smaller control wires. It looks like a "normal" solenoid with a cap on one end which is the latching part. This is a common failure part.
Use a voltmeter and if you have 12V on one side and not the other then you can bypass the solenoid and replace later or not at all.
My prior RV turned off all house power with this switch while the current RV does not turn off the refer.