I installed 2 FF in my Class C.
One in the bathroom where there was only a small fan, the power was there so it was an easy mode.
The other was towards the front and below is about what I had to do.
You should be able to remove the inside plastic shroud for the vent and look and see if there is power routed to it. If not you may have a light close to the vent and could try to pull a wire from the light.
In most cases the RV's have power routed to the vent location as if they install the FF as an option they want to have it prewired.
2002 Monaco Windsor 38 PKD
2005 Jeep Grand Cherokee w/5.7 Hemi