Hi Steve...welcome to the Forum!
Like yourself, I have driven quite a lot of Europe, but never driven Portugal.
I've been to the Algarve and travelled by train across it (the scenery didn't really change at all...quite barren really!) but thought of riding my motorbike down there. Planned to ride down through France, Spain and then into Portugal so no ferries apart from Poole-Cherbourg. You can always travel to Northern Spain by ferry but much nicer driving it, I think.
What convertible are you driving there?
Regards, Trevor - Admin