"Enter your date of travel on the Interbus site along with Aeroporto Palermo and Trapani - 9.30, 13.30, 15.30, 18.30, 21.30"
Ciao Vagabonda, I copied the above from one of your post, (it's been deleted, because because it's too old).
Is this schedule for the summer?
I've looked at the Interbus web site, and I could only go as far as Feb, and there're only two departures a day from the airport.
Hopefully there'd be more in Sept. Palermo is a convenient airport from Rome. There're almost hourly flights from Alitalia.