Yep same here , replaced small fan in Bathroom with a Fantastic Fan and then the other one over the rear bed . If memory serves me right I had to snake wires over to the one above the bed .
The front vent that was up over the cab part on both C's neither had wiring and had a solid beam/track across .
If the over-cab part has a light mounted up there , a person could (might) snake wires from the light ?
If you do get the fan('s) get the ones with a thermostat setting on them.
We'd park somewhere ,crack open the vents dial one of the fans thermostat then as it heated up in the RV the fan would would cycle on. Helping to cool the inside.