Having driven that road myself the one catch is that as you get nearer and nearer to the border so the signing for the border gets less and less. When you get to Irun it is non existent! Hope you have a good GPS! Also Bilbao to Bordeaux is around 340Km or about 210miles and it is not easy driving.
There are many itinerants around Bordeaux so whilst it is an interesting city you might do well to find a campsite outside its boundaries. There is a very good tram service around the whole Bordeaux area. Don't forget to visit St Emilion - lovely town and superb (mostly red) wine E of the City, and the Medoc wine region on the west bank of the Girande but effectively N or NNW of the city.