Spain in a Flexwing
Down to Spain in a Flexwing (edited highlights from my trip down to the World Champs in Aug 2012).
A really good jumping off point in southern France is “Base ULM St Exupry” at Montpezat. They are very helpful and welcoming. They sell Mogas and you can camp. I tried to get him to file a flight plan for me but he didn't know how. The problem with not having a flight plan is that you then can't receive a FIS and that means you really are on your own crossing the mountains.
The nearest French airfield to the Pyrenees is LFCO Oloron. They are friendly and helpful and sell Avgas. I don't know if you can camp there but there's a lot of space so I can't imagine it would be a problem. I passed through on a Monday which is a good sign because plenty of French municipal airfields are closed on a Monday.
There are two mountain crossings that I know about. On my way south the weather was deteriorating from the west and I went south over LFIM St Gaudens and followed the road to Bagners de Luchon. This was a very scary crossing. You pass over the town in a narrowing valley. Beyond the town the valley turns right, that's the way up to Peyresourde but it's a blind end. Immediately before the right turn there is a saddle on your left with a tiny road going over it. That's the pass you need. It's at about 7500'. It leads to a valley that goes Southeast (ish). Once you're in that valley you are in Spain and it gets wider and lower and leads in a very obvious way down onto the plain. On the map this is the valley that run between LFCB Luchon and LESU Pirineus.
The other crossing that I know about is St Jean de Pied Pont which is a lot further west (and a lot lower). If weather is not a problem this is the one to go for. It's a piece of cake compared to further east. From the north it's easy you just find the town and follow the road south. From the south you have to pick the valley with the old road not the one with the new road. The valley with the new road ends in a mountain with the road going into a tunnel :-)
In general, as far as I can see (speaking as a beginner) the air is either moving North or South. If it's moving North then the French side will be in sunshine and the Spanish side will be in cloud. If the air is moving South then the French side will be in cloud and the Spanish side will be sunny. This is what stops you just going over the top. I know plenty of people who have just gone up to 15000' and taken a straight line. Personally I don't own a moving map GPS so I read the map and follow the road.
On the Spanish side the big airfield that everyone goes to is LECI Santa Cilia de Jaca. I haven't stopped there but it is known to have avgas and a restaurant. It was closed for a model plane event the weekend when we all went south so I can't say if you could camp there. I can say, it's huge, it's about 10k from the nearest town and it's in amongst the mountains. If it's open it's about the only place that's feasible to close a flight plan (unless you can do it by radio).
Further west the choice is LESG Sanguesa or Lumbier. Both at the western end of the big reservoir, “Embalse de Yesa”. Sanguesa is almost abandoned. A dirt runway covered in thorn bushes. The big plus point is that it's only 1k from the village which has a petrol station. If you need fuel you have to go here. Lumbier is a big place with a tarmac runway (not perfect but OK) a clubhouse and lots of hangers. The trouble is there is no fuel and the nearest petrol station is 12k away! During the week it's likely to be deserted and locked up. There are a lot of bungalows on site and the caretaker lives in one of them. His name is Habi (Javier?). He may be able to unlock the clubhouse for you but that isn't going to get you fuel.
Further south there is LEGY Garray. This is big and new and modern. It has Mogas (ask for it and he gets a bowser out of a lock-up), food, bar, etc. The downside is that the guy who mans the place is a rip-off artist and you're a sitting duck. He has a special landing fee for foreigners and he won't let you camp but offers to take you to a hotel in town.
I've flown over both LETP Santo Tome and LECA La Nava. One of then has a tarmac runway but I can't for the life of me remember which. They both looked deserted both times I went over. Near to Segovia is Marugan and LEFM Fuentemilanos. Marugan is big and modern with bar restaurant and pool and Mogas. It has lots of space for camping but I don't know what the attitude to that is. The owner is friendly but avoid his wife :-). Fuentemilanos is a big gliding centre and has a proper campsite.