Hi,
My Fleetwood Bounder had 12 volt power to all of the vents, even though only the bathroom had a small and noisy electric fan installed at the factory. I guess that Fleetwood expected their dealerships to be able to install these as a option and installed the wires at the factory on all of the Bounder lineup.
Have you removed the inside vent cover and looked for wires?
Do you have a light within about 3 feet? If you can remove that light fixture, and then using a coat hanger, run wire between them, it will work. You only need #16 gauge wire. If you do not have any wire sitting around the house, a small extension cord (kind you get at Dollar Tree to plug in a electric Christmas tree will work fine) and cut off both ends, use only the wire.
My 'attic' is all foam. I was trying to figure out how to run the wires through it before finding them factory installed. Once the vent cover is totally out of the hole, you can use a long drill bit to drill a hole through the styrofoam towards the light fixture. Yet you must also avoid all existing wires (cutting through them would be bad) by just using the drill bit as a knife.
For my automatic satellite dish, I installed the dish above my ducted air conditioner air duct. Then I ran all the wires through that air duct. It went all the way toward the TV set, and I drilled a hole above the TV into the space behind the TV, then ran the wires back there, to the receiver. On the roof, I drilled a hole into the air duct through the roof, and sealed it with rubber roof sealant, then ran the wires under the dish, protected from the rain. It all worked out pretty well.
My A/C ducts also lined up with the roof vents, so it probably would be possible to use those as a pulling chase for new wires too.
Also most Fleetwoods have a removable cover where the wall meets the roof. This is where I ran new wiring for the inverter, rear camera, ect. The Factory runs wires there for everything from the electrical panel to the microwave, speaker wires, 12 volt ceiling lights, ect.
The fantastic fans only draw about 3.3 amps on high fan speed, so you do not need 15 amp rated #14 wire. #16 should be used just because anything smaller would have a lot of resistance in it, with only 12 volts to start with, you do not want to run to small of wire.
Good luck on your project.
Fred.