Having installed many ceiling lights and fans in homes, the only way I can see you installing a ceiling fan in the RV would be a ceiling panel removal. That would get you to the rafters to mount the electrical box and MAYBE allow you access to a side panel where you might get a fish tape down a wall to the underbelly. From there to the electrical panel.
I am sure it can be done depending on the amount of labor and time you wish to put into the project. It seems like a lot of work.
An alternative might be a straight ceiling mount with a swag chain from the fan to the wall plug. Not as nice and neat but would work.