In reply to oliwarlow: From memory the best and easiest car park to use is down on the pier a few mins from the terminal (on the left of the access rod), it isn't free but given I've used it a few times means it's probably pretty cheap (I'm thinking it was only a few quid for several days), the alternative is somewhere back in the town and that's going to be a pretty decent walk to the terminal especially if your carrying gear, I'd just head down to the terminal and see what you think, if the car parking charges are prohibitive just work back towards the town and see what crops up.
Liam