Four 14 day cruises can get you $1000 in OBC and often b2b cruises can work the same. Longer cruises often cost less per day than shorter cruises, can be more interesting, and have fewer kids.
Nothing says you have to hold the stock forever; you can buy and sell as often as you like, subject to things like wash sales, etc.
Whoever owns the stock has to be an occupant in the cabin that gets the OBC.