My advice would be to rent. The cruise is a special event and it is obvious from your question that you would lie to do it right. Sure you could do a conversion but you have the real thing coming so you don't have need of a conversion that may or may not turn out the way you want. Also do you really want to spend pre-holiday time trying to figure this out. One or two calls to one of the vendors here, that deal in rentals, and you are all done.