First trip to Spain and Portugal - advice please

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Hi , we are new to campervan touring and are about to go on our first trip to Spain and Portugal - we get off the ferry in Bilbao . It is obviously low season and many sites are closed . Has anyone any advice about good sites or safe free areas ( though not confident on this at the moment) We have read the club advice. We are free to travel anywhere with only a couple of nights booked outside Madrid at the moment. All advice and ideas appreciated