Most travellers from the UK heading to Morocco in the cooler months take the ferries from Portsmouth to northern Spain: Bilbao or better still Santander. When you add up tolls and fuel and time across France it works out the same price for less driving or riding.
The Brittany ferries on this route are well-equipped cruise ships with plenty to occupy you over 22 hours at sea while doing a great job of smoothing the voyage across the Bay of Biscay.
From Santander to Algeciras near Gibraltar (the most used port) is about 1000km, and the empty and fast network of roads west of Madrid (A67, A62, A66 and A381) can get you between the two ports in one long day if you wish. The only short section of toll (peaje) is south of Seville.
Moroccan port maps