Hi,
I have a 97 Fleetwood Bounder, and they did install 12 volt power to each roof vent. I changed all 3 of mine to Fanstastic fans when my RV was new. I just bought another one from Amazon.com for my other van, and will get it on the 4th. It was only $160 for a manual open, reversible fan.
You can remove the inside cover, and look for 2 wires. They normally install the wiring, and then the dealerships will install fans at a later date. Some even install a romex wire for a optional 120 volt A/C unit too, so do not mix up the wires.
Or you can 'fish' a wire from a nearby light fixture that is on all the time.
I also have a pair of 120 watt solar panels to power the fans all day long. They also shade a portion of my roof too!
SunElec.com sells a 140 watt panel for $229. You can get a PWM controller for about $35. UV rated grey romex from Home Depot. 2" angle aluminum to make mounts that will allow the panel to sit about 1" off the roof, the cool air keeps it cooler, so you get more amps out of the panels.
Some rubber roof sealant between the mounts and roof, and over the screws, and you are done!
Good luck on your project!
Fred.