I believe I am correct that topless sunbathing is not permitted on RCI caribbean sailings, european sailings yes. I dont know what your itenerary is but you shouldnt have a problem finding a place to to bronze topless in the southern caribbean.
If one of your ports is St. Maarten, you can go to Orient Beach. They have a clothing optional area. Never been there myself.....always found it difficult to suck in my stomach and talk at the same time.
Serenade of the Seas b2b January 2016
Serenade of the Seas b2b January 2017