We've travelled on Tirennia ferries from Civitavecchia to Sardinia and return, with a car, and from Naples to Sicily, then Sicily via the islands back to Naples. This last journey took a week because we stopped off on the islands to spend a day or two on each. In all these trips, the ferries have been on time and clean and comfortable. Depending on what time of year you travel, the ferries can be very crowded, especially in August when the Italians are travelling. We've usually taken the morning ferries so finding a place to plant is relatively easy. You won't have a car, I presume from your e-mail, so the line-up won't be a problem for you.

We haven't taken ferries to Tunisia, but did take one from Catania in Sicily to Malta and back again. They too were busy but each time we parked on a deck with our wine and food and had a comfortable trip - even though we were suffering from a bout of food poisoning and feeling very weak. Again, it depends on what time of year you're travelling. The only downside for us, was the departure from Catania (late in the afternoon) which arrived in Malta at 3:00 a.m.! We had no hotel reservations but fortunately, we were befriended by an English couple who had been on the island many times before, did have a hotel reservation, and convinced the hotelier that he could find a room for us at the ridiculous hour of arrival. The moral, check the time of arrival at your destination and have a reservation, or meet some friendly travellers who can help out!

In all instances, we didn't buy tickets beforehand. Just showed up at the ticket office and bought. Some of the ziners in Italy, or with more travel experiences on this leg of your travels, may have more insight into reserving beforehand.

What I have always loved about taking the ferries is the interval between departure and arrival. Boats allow you to slow down and enjoy the getting there.

Have a great time.

Lucy

P.S. If your schedule is flexible enough, I'd strongly encourage you to stop over on Stromboli. Little electricity at night, sitting in THE (only) cafe on the harbour and watching the ferry arrive and depart, climbing the volcano...what a great break.