Well the one thing to consider is wiring. Yes, a big part of the coaches wires, run inside the roof. In your case, if there is a wiring harness close to your existing vent to steal power from, you will be better off. You still need to "fish" wires over to/thru the wall to have a wall mounted switch though. Can be tough, certainly not impossible. However, as Johno02 said. In a 5er, the ceilings can be way up there, and putting the work in to a wall switch will pay dividends at first use.. I do like navegator's idea alot. I think that would be my choice.