A friend from Morrisville PA (north of Philly and sort of across from Trenton) bought 35 acres in Somerset County, Maryland in 1998, built a home, and has lived there ever since. He gigs for a living all points south to S.C. and a bit west. His "developed" accent is as thick and even more so. As a musician, the mimicry-gene is dominant.
Speaking of accents: I've run into landlocked Tidewater accented people in central Delaware and always thought it was a remnant of Thames oystermen's accents who settled up the Chesapeake but this Crisfield buddy says it is Tidewater - Older Southern American English. The study of dialect & migration is like a history lesson. Neat stuff.