We stayed at a lovely site in Orio about 30Km west of San Sebastián. Highly recommend it, right next to a small but nice beach, lovely town, great walks around the town, and a train station that you can get to San Sebastián or to Bilbao.
https://oriokanpina.com/en/ And if you have the ACSI guide it's in there. Good facilities and spotless site.
We also stayed at a great aire in Bilbao, it's on the hill outside Bilbao and is a great facility. There is a bus stop right outside which goes right into the city centre for €2.50. We stayed two nights, there is a bar just up the road from it which has a huge restaurant, basic but good quality food, worth visiting. Search for campercontact.com and look for site 10426 or municipal motor caravan park.
Bilbao was great so definitely recommend a stopover there!
Have a great trip.