We went to Orkney in 2005, booked through Carefree in c and cc. No problems at all with bookings. Travelled on ferry from Scrabster to Stromness (very nice modern ship).
We also stayed at The Pickaquoy site in Kirkwall, which is near to the Town, but far enough away to be quiet.
Unfortunately, we were unlucky enough to pick the week when the Scottish Sheep Dog Competition was being held, at our site!
This meant a lot of noise from the dogs (some with 5 or 6 per Unit!), and we were glad to see the back of them, but unfortunately this was not until the Wednesday (we were there Sat-Sat).
Orkney is really lovely and worth the effort to get there - no probs with a caravan at all, but I think just the 2 sites, one in Stromness (lovely location overloking the Bay) and Kirkwall.
But if you go in August, checdk first regarding the dog show, unless you enjoy endless yapping and Barbara Woodhouse look-a-likes!