Sadly I can't come on the trip (maybe next year!), but can recommend the camp site at Bryher. We made use of their facilities last year whilst anchored in Green Bay, and a friend who was born on the islands has been camping there every year for the past 20 years!
If you don't mind taking the ground, Green Bay is a superbly protected anchorage for most conditions. Failing that there's visitors moorings owned by the Tresco Estate between Bryher and Tresco, which incur a daily charge (£15ish I think).
An easy dinghy ride (or even swim!) between Bryher and Tresco, just watch out for the high speed passenger ferries that don't appear to slow down... Tresco Stores has most provisions you might want, although at slightly elevated prices. Between Fraggle Rock and Hell Bay Hotel on Bryher, the various places who's names I forget on Tresco, and all the honesty boxes around, food shouldn't be a problem!
Look forward to seeing some photos!