If you are planning on traveling from mainland Italy to Sicily you might want to consider a car ferry from Naples to Catania or Palermo.  It is a long drive from Naples and still requires a short ferry ride to Messina if you drive.  The car ferry ride is 11 to 12 hours, usually overnight.  The ferries have small but comfortable cabins for up to 4 people with a small private bath with shower.  The rate is cheaper than flying and a lot less hassel than the airport.  You can buy tickets on line from the major ferry companies (Caronte and Tourist, Grimaldi LInes, and TTTlines are three such companies) and should probably do this several months in advance.  The ticketing process asks for make of car and license plate number, but you can put in a model similar to what you will be renting and put rental in the box for the plate number. You must print your tickets to take on your trip. There are 2 copies and you will need them both.

The ferries carry mostly trucks so the cars are last to board. You do not need to arrive earlier than indicated on your ticket. It was fairly easy to find the embarcation point in Naples, so just get good google directions.  The ferry also has a basic restaurant so you can have dinner on board.  SOmeone comes through and knocks on your door to wake you up in time to have a shower before you arrive at your port in Sicily!