I've just heard about this event - sounds great. My friends English Heretic and Haunted Shoreline should be appearing. Many childhood holidays were spent on a caravan site next to the fort, which in those days was derelict and dangerous and became a site of fascination for me. More here.
Author of Subterranean City, Beneath the Streets of London, London's Coffee Houses, Decadent London, The Folklore of London, Subterranean City (Revised and Expanded Edition), Netherwood, Last Resort of Aleister Crowley, Lord of Strange Deaths, the Fiendish World of Sax Rohmer; Secret Tunnels in England, Folklore and Fact