Used to live there. The ferry trip across in expensive - steam packet company, but once you are on the island it is very nice. Kinda like putting all of the best parts if the UK, scenery wise, into one small area. There is a nice place to camp in sulby, a field just opposite the pub that lies other side of the sulby straight.
Glen Maye also has an awesome pub for summer afternoons. If you like Mountain biking or road cycling then pack the bikes too as there is fantastic riding there. Think my bicycles got more mileage than my car while I was there.
Their is a local VW group over there and they can give you some up to date campsite listing and perhaps host you.
Enjoy, well worth a trip