Hi jenspen
Ive stayed on the site at lochranza, its called Lochranza golf, you dont need to play golf.
If you book the site through them you will get a deal on the return ferry crossing and your site.
This area of Arran is brilliant for wildlife, you get the golden eagle up behind the distillery, otters near the corrie ferry, deer come roaming onto the site in the evening and seals are pretty much all round the island.
We stayed on the site and occasionally wild camped at different places around Arran. As long as you are considerate where you park no one seems to mind.
Drive around the island,(just one road around the perimeter and one road through it), and you will see many places to stay.
Its like going back in time, apart from Brodick the main place where you get off the ferry from Ardrossan, there is no traffic lights. there is no parking charges,its all so laid back, the perfect place to chill out.