I used to run trips around Morocco (actually, I preferred Tunisia & Libya) but haven't been there in over ten years.
I did the Portsmouth to Bilbao ferry once - it was like a prison ship, full of Geordies on a 'mini-cruise, with 'cabaret' and other entertainment, usually people sliding down the bar or passed out in the toilets. If you use this, I'd suggest locking yourself in your cabin with a bottle of something strong enough to sleep through....
It's much more enjoyable to drive through France & Spain (France of course, is put there solely as a means of getting somewhere better, hence the excellent roads) and staying at 'Mercure' type cheap hotels or campsites. As above, I used to get the Algeciras - Ceuta ferry, reasonably cheap & quick, but as I say, I've not used it for a while. We used to stay in one of the hotels in Ceuta and cross over the border early in the morning whilst the touts were still asleep - I believe you can now do the entry cards online.
I know of people that have done the Tangiers ferry port and apparently you need a lot of time to get through the bribe-takers & tat-sellers.
It may be worth having a look on
https://www.horizonsunlimited.com/hubb/ it's mainly centred around two wheeled vehicles but there's a lot of good info on there and the travel info is about as up to date as you'll get anywhere. There is (or was) a campsite in the middle of Fes, actually in a walled military camp that is a good 'end of day 1' location, with rudimentary showers and toilets - but you can go outside the walls into Fes in taxis knowing your vehicles & tents will be relatively safe. Meknes also has some good traveller hotels with secure parking.
Along with the locations mentioned in the posts above, The Atlas mountains need exploring and Zagora is good for some dune-bashing, wherever you go, don't do it as a single vehicle and be very aware of what and who is around you - don't be tempted to cross into Algeria, even by accident.
The 'street kids' will try and open your car doors, steal anything and throw stones at you!. The police are similar, often being quite insistent on the need for a 'petit cadeau' as a requirement to carry on your journey. Sometimes a shiny pen, is enough to distract them, along with your other vehicles causing a blockage behind you - along with the 'Gallic shrug and hands in the air to indicate you don't understand.... The military checkpoints are always best approached slowly and with big smiles and waves, they're actually the 'good guys' in that they will report your registration no's and direction of travel, if other checkpoints don't see you, they'll come looking. I always used to have a brief and reasonably vague itinerary printed out with dates, camp sites / hotels etc. on one side and names, DoB's nationalities and vehicle registrations on the other, the idea was to give them out to checkpoints we had to stop at as a means of making their job easier, and therefore quicker for us to get going again. I'm sure there's more, lots more, I could mention but as I said, it'll be rather dated.
