Watson Bay is where Paradise Garage sits. That garage belongs with the Dominator buggy, and it has a gun locker plus a place to fence stolen goods.
Rockstar's Ultimate text says you can 'conveniently store' the '67 Dominator Buggy at the Paradise Garage in Watson Bay. That garage also 'features a weapon locker plus a secure place to deposit stolen goods to be fenced.'
Some fan maps place Watson Bay on the Gulf coast. Others leave it unplaced, which is the honest position until Rockstar shows a map.