Congrats! If I were you, I would have a chat with the cruise director, to advise you, where the best, or most fun or most romantic,or less crowded place to pop the question should be. I bet he even might have a few ideas up his sleeve, to even make this wonderful moment even "more" memorable. You're not the first to do this, so his imput could really be helpful!
I'll say, get a table for two, in a special dining venue, get on one knee,and pull out the bling.