Bilbao docks

We're planning a bit of winter sushine, crossing to Bilbao at the end of January before towing South. The ferry gets in at 18:00 and I see from the Brittany Ferries web site that it is possible to stay overninght in the docks. I read on other fora that this isn't your average ferryport but a full-blown commercial port with all the attendant security. Does anyone have any experience of how safe it is to overnight there?