We toured the Pyrenees & Picos in 2019. We didn't really struggle to get fuel although al the cars in our group could manage 300+ miles between top-ups.
One thing we were advised was that if you stop in Andorra, only book one night. That advice proved to be good. There is very little there in the summer - apart from cheaper petrol.
Our route was Bilbao, Donostia (worth 2 nights - lovely city to walk round), Lescar, Andorra, Arties, Sos del Rey Catolico, Santo Domingo de la Calzada, Cervera de Pisuerga, Cangas de Onis, Santillana del Mar, Bilbao
Where practicable we stayed in Paradors - they were all excellent although dinner service isn't usually available until 8pm or 8:30pm which can be an issue for those used to dining earlier.
Do make sure you understand the road symbols on a Spanish map - we spent a half day on something resembling a gravel track taking a scenic route.
