Fantastic Fans run on your battery. If your old vent had a fan, then the wiring is already there. If it didn't have a fan...it may also already be there in newer trailers - alot of them were pre-wired. If there isn't power, then you can run it in the ceiling down the wall without too much trouble if there isn't a ceiling light nearby. We just ran Romex for our second fan in our Safari across the ceiling and down the wall. I was really surprised how easy it was...I was expecting cross member supports (running the length of the trailer in the ceiling) interfering...but there were none.
You'll most likely will have to remove your old vent/fan in order to tell it it is pre-wired or there are other accessible wires nearby.
As an alternate, you could attend an International or Regional WBCCI Rally - Fantastic Fan always has reps & installers there to install them for rally attendees. That's what we did with our first one.