From what I've heard, working for Steiner can be tough, mostly in the way of hours. And hours for trainers can be just as brutal as hours for massage therapists.
I don't want to discourage you, I just want you to be aware of what you may get into. If you interview as a trainer, be sure you ask them what a typical day looks like for you. On a ship I was on last year, there were two trainers and the hours were ok, but then one left and they had no replacement. The lone trainer had to work every morning 6am until the other one came (about a month later). She was not a happy camper.
As far as money I have no idea what the commission structure looks like. I've heard people say they make a boatload and some say they just get by - I guess it depends on how good you are at your job.
Hope this helps. Either way, do it for a contract. Ship life is fantastic and you should experience it once in your life if you can! :-)