I can just corroborate, in broken English, all said above.
- Moroccan customs do check the green paper when you come from E.U! In case you plan to go back to Africa
And sometimes when you enter from RIM. ( a good xerox job in Ndb can do the trick)
- The friendly Guardia Civil very rarely check the green paper in customs, (specially if you look fine, according to their conservative standards), they are more interested in psychoactive botanical samples.
Despise that, being insurance-less in Spanish roads is far too risky. They often do check papers. Having U.S. plates you may show any paper with the good dates and the word insurance on it, but If you get hit, the other party insurance has no obligation to pay, and you get a 950 eu fine.
- I don't know what is best If you plan to stay in E.U. for short time, my insurance company knows nothing about short time insurance. Sooner or later you got to get it wright. Expect no kind of help from U.S. embassy even if things go wrong. May be best try to get and extension of your U.S. insurance.
If there is such a thing as advice: I'd spend the money in insurance and take the road north, in stead of the expensive ferry. Keep in mind that a decent European insurance company can help you also if you go back to Africa. They paid my many thousand eu medical bill in Dakar.
Send me a mail when you are around here.