I have a few letters in a book, Antibellum Pensacola and the Military Presence, by Ernerst F. Dibble that show this. There are also more found in the Board of Navy Commissioners papers at the National Archives Office of Naval Collections.

There's one interesting one from Stephen R. Mallory on the treatment of one of his slaves. Seems he felt it harsh. The practice of using slave labor continued when the US took over the Florida territory. It began with the Spanish then British, French and so forth. They used slave labor for Ft Jefferson also. I would assume that it was common to use them at all US built forts when available.

Pam