Rans6...
Forget about San Sebastian or Vitoria. Microlights are not allowed to use controlled airfields in Spain.
Nogaro LFCN looks like a a good 'base camp' for crossing "the hills". There is a camping site 50 mts from the aerodrome and a selection of hotels nearby.
bienvenue Nogaro (Gascogne, France), ville de l'aroclub du Bas Armagnac base de planeurs, avions, hlicoptres, ULMs et Autogires
The guys on the AEPAL (Spanish micro assoc) forum, say it is a good idea to make the first landing in Spain at a field with an ICAO designator, because using ZZZZ and Remarks on a FPL has been known to cause problems. That is a shame, because Lumbier looks like a nice airfield. The closest seems to be Sanguesa LESG, but on YouTube it looks like a field in the middle of knowhere. On a straight line from Nogaro to Sanguesa SD stipulates a MSA of 7200'.
Have you got a transpoder?