Arrival at Santander Port

Hi - we arrrive at Santander Port at 18.15 hours on November 4th.  We are travelling over to stay in Benicassim for 2 months.  We have never been to this port before and wonder if there is a place to 'stop overnight' before travelling onwards early on the 5th.  We had been looking at an overnight stop in a campsite near  Castro Urdiales, and have enquired but have received no details as to whether they would be open for booking in during the evening, and we do wish to move on early -maybe before the office opened so need to pay on arrival for one night's stay.

many thanks.