Sounds like a door switch to me, too. My 2013 Mercedes Sprinter chassis uses magnetic proximity switches. I don't know if later versions of Ford chassis do or not. You s/b able to tell by opening the doors and check for a "plunger" type switch (usually located in hinge area of door) or a round flat button-like device (usually located at the rear of the door). If you have magnetic switches, make sure they are free of dirt build-up, no label or tape over them or the area of the door that mates with it. Also, check how tightly the doors close. If a door seems slightly open yet snug with the latch, the latch stub (pin on the body side of door) may need adjusted.
With the doors closed solidly, try tapping or bumping each door to see if you can determine which door might be causing it. If you can determine a specific door and there is no excessive dirt as described above, then you will probably have to remove the switch(es) and check for bad connections. Even if you decide to take your RV to a Ford dealer or automotive servicer, it might help keep costs down if you can narrow down the location of the problem so the servicer won't spend so much troubleshooting time on it.