I'd take the events described in “Dunwood” & then take grab my copy of the classic
L1 The Secret of Bone Hill By Lenard Lakofka & flesh out more of the region described in the book then set it around Lenore isles. Yes I know that the village of the fishing port of Restenford described in L1 The Secret of Bone Hill has been used as stand in for Saltmarsh village in the past.
By taking Ghosts of Saltmarsh & setting within Brigand's Bay from AS&SH we get a dangerous situation in which the Deep Ones of "Dunwood” are encroaching dangerously close to the Hyperborean capital city & its environs. Do you want even more detail for the areas around 'Dunwood'? Well earlier I mentioned L1 The Secret of Bone Hill By Lenard Lakofka . Well for years now Lenard Lakofka has been doing some excellent free campaign expansions for the Lenore Islands on Dragon's Foot called the Kroten Campaign Companion for the L5 module.
"This manual describes the Town of Kroten and the nearby area, which is located on Lendore Isle in the World of Greyhawk. Details include nomenclature used by the author, world background, and local features. Also included is a detailed description of the Town of Kroten, excepting three key areas: The Fane of Syrul, the Fane of Pyremius, and the Castle Kroten itself. These areas are described in L5B: The Kroten Adventures"
This material makes an excellent background setting for Ghosts of Saltmarsh or the original U1 The Sinister Secret of Salt Marsh adventure for first edition AD&D. The fact is that there's plenty of material here to lay out many years worth of an epic campaign. In point of fact this entire adventure arch would make an excellent Castles & Crusade or Dungeon Crawl Classics adventure having the PC's surviving on of the earlier raids on their villages. They survive to take up the life of an adventurer.