Lee,
RIAT relys on literally thousands of volunteers, who are accomodated in barrack accomodation, working for anything between a couple of days and several weeks.
You're probably too late for this year (unless you have some skill that's in short supply!), but there's no harm in trying. RAF Benevolent Fund Enterprises are on:
01285-713300
www.rafbfe.co.uk
Failing that, there are usually loads of camp sites...