In reply to jon59:
I've camped in the pay per pitch campsite in Glen Rosa. I don't rate it. It's ned infested in good weather and the facilities are poor.
Camping at low level in Arran at this time of year will depend on a good breeze to blow midges and clegs away.
My favourite option is to bivi up at a nice grassy area just West of the summit of Cir Mhor. Up there you have the least chance of being midged as there should be a breeze most of the time. The walk in to Cir Mhor is about 2.5 hours up Glen Rosa.
Don't bother taking your van over. It's fairly expensive for such a short trip. Enjoy- the Rosa Pinnacle is absolutely superb.