Santander Ferry Arrival 5.15pm - Site for evening?

In mid-April we will dock in Santander on the Pont Aven at 5.15pm, presumably along with lots of other outfits.  Naturally, arriving at such a time means finding a site within fairly close range.  The C Club Spain Guide lists Camping Cabo Mayor in Santander (6km NW) and Camping Altamira in Santillana del Mar. The ACSI 2013 book lists No. 2215 Playa de Oyambre (Cat. 1) at S. Vicente de la Barquera as the nearest.  These seem to be the only ones that do not have the caveat "not suitable large outfits" and we have a 7.2m Senator Oklahoma.

Recommendations for the first night stop welcomed!