Done Spain from Scotland a couple of times, I found the best facilities for overnighting and reasonable landing fees on the way down were any of the following : Jersey, Rennes, San Sebastián, Pamplona , LEAX (aero club Malaga) . 2 really good GA fields I overnighted at in Portugal were Portimao in the South and Cascias for Lisbon. While in Spain I based myself out of LEAX and done day trips up the coast to small microlight fields although not sure they'd be long enough for a loaded up 172, I was flying the Maule. I started out planning on a Morocco trip but got bogged down in paperwork and agents etc. and that was before I'd even left Spain. Not suggesting it but I sometimes wonder if I'd just taken off from one of the uncontrolled microlight fields headed across the drink and called up the Moroccan tower 10 miles out what would have been the deal.
The Malaga flying club LEAX are very GA friendly