Ha..this is funny.. as an ex-navy brat that was there in the 80's I ran all over the place out there. The bunkers were all storage areas used by the MOMAG unit(mobile mine assemby group), no secret tunnels or underground bunkers to be found. The Gaydon Hangar was just that.. a big hangar, if I remember right it was mostly RAF personel/contractors in that hangar, the team was in the long building next door. Used to ride my bike in the hangar.
Those that remember the movie White Nights(
http://www.imdb.com/title/tt0090319/) was filmed out there, the fake 747 they blew up for that was hosted in that hanger, along with all the movie crews for how ever many months they were out there.
The "Brown Structure, use unknown" on that site was the chute loft(For drying/hanging/repairing parachutes), supply and gym/training area/showers for the SEALS, the 2 large garage doors behind it were where the SEAFOX(
http://www.warboats.org/seafox.htm) boat was stored/worked on, along with a few other offices.