In reply to Harry Jarvis:
Hi Harry hope you are doing well.
I was on Arran in May last year, stayed at seal shore for 5 nights. A nice site right on the shore, with reasonable facilities. More vans than tents when I was there, but that wasn't a problem.
Only downside is it's a bit of a drive (30 mins? each way) up to the mountains, although there are plenty of nice coastal and low level walks.
Glen Rosa campsite is in a beautiful spot and great if you want to get up onto the mountains, I walked past it twice on my way up to or out of the mountains, but I didn't stay there. I think it is cheap but basic.
Martin