Ideally a garment bag with the dresses covered in plastic from the dry cleaners will be your best bet.
If your luggage limit is restricted , get some of the same plastic bags mentioned above and lay the dress out on a flat surface and cover with the plastic.
Roll the dress with the plastic and the plastic should help to keep out the wrinkles.
For packing in a suitcase, you can also use tissue paper.
I have done this frequently when we have gone on cruises and found the plastic to work better than tissue paper. Besides the fact I had the plastic around, but to use the tissue paper, I had to go out and buy it.
We fly a lot Heidi and many times it is not possible to hang a garment bag in the First Class Closet. The closets are tiny and many times the crew uses the closet which if they do allow the garment bag if there is room, the dresses would get squeezed in. Plus the closets are short so you are bound to get wrikles. My suggestion is to purchase a small steamer that will do the trick. Or, just hang the dress on the back of the bathroom door inside the bathroom, turn on the shower on hot to make a lot of steam and close the door. Last suggestion is to fold each dress neatly in between tissue paper with the cleaner plastic over the dress. I do this all the time and it works for me. Have a great time in Aruba :-).