Hi, we’ve tried this, unfortunately they are fully booked! But thank you for your suggestion.There is a campsite, literally a few hundred metres from the ferry terminal.
It's called Bella Riva, and is an ACSI site (958) as well.
They are well used to people arriving off the ferry. They leave an envelope with your pitch info sellotaped to the door into reception. Pitch up and pay the next morning (or in advance of course) They also take CMC vouchers.
We have used it, nothing brilliant, but REALLY handy for the ferry.