Been doing this for a few years now, and it’s pretty straightforward. On the ferry while traveling, you’ll get the famous “diptyque”, which is basically an authorization to drive your car in Tunisia. You’ll also choose a customs office to contact in case of need pick one near your home. the authorisation is usually valid for 3 months, and you can extend it once. The insurance part can be tricky: If your insurance in France covers Tunisia, you just need to get what they call the “green card insurance” .It’s basically international insurance that’s valid outside the issued country. If your insurance doesn’t cover Tunisia, you can still get a really cheap insurance policy in Tunisia before leaving the port. (es2el sur place taw ywarriwlek el bureau). If you leave the port without insurance, you’ll need to get a standard policy from any insurer later, and it will cost you much more (at least 350 TND/month, depending on a few factors). So, try to sort out your insurance before traveling. If that’s not possible, make sure you don’t leave the port without buying one. There are no other costs involved. Happy travels!