My post probably won't help you much, but, here goes . . . I don't go to the Carribean much, but, from what I've read here, most Carribean routes aren't Medallion heavy, but of course, with a companion, you'll have to wait til the last minute to find out if you get it or not. That said, may I suggest that you publish the specific route you're flying so that someone here can have a better shot at helping.

Just a side note . . . I re-read your post to see that you used SM for the tix. Can you get a companion upgrade with award tix?