We left that Bilbao ferry at about 0830 one Monday in April 2000, and it was my first time towing abroad. The plod through the dock area is useful for orientation (very cheap diesel available on the dock road) and the signposts to the motorway must have been OK because we got there without any problems.
A few years later, having done Calais, St Malo and Dunkerque I would say that Bilbao is no worse than any other port. Calais is the easiest because of the road layout and immediate access to dual carriageway, but Bilbao was very manageable.