I'm spanish from Barcelona and I can help you if you need translation or so.
I go once or twice a year to Morocco, but I ride my bike all the way down or I take a Ferry from Barcelona to Tanger, but some friends of mine go with the car and trailer and they allways cross the border with the car and then they find some place in a Hotel or so to park both the car and trailer, Morocco is a truly safe place. If you want a kind of western assitance and parking you may contact contact Assitance Secours Rapide in Morocco
http://asra.assistance.ifrance.com/topic/index.html
They have safe places to keep your car and belongings, contact them before and close a deal.
I do have some friends in Ceuta (Spanish city on the African side)
http://en.wikipedia.org/wiki/Ceuta
I can contact them if you want to go the Ceuti way adn keep the car on the spanish side of Africa. Honestly border crossing at Nador or Tanger is a lot faster -they are really slow, but Ceuta is pathetic-
If you want to find a parking in south spain for the car and trailer, find a "Parking de Caravanas y remolques" at the city of your choice, it is safe and a lot cheaper than Campings or so. A search for them at google.es will help you.
Last may with my DRZ helping some guys on the Rift mountains
and others guys helping me
have fun,
j.