Why not just plan on using the disposable Platex liners for the week?
Of course your child might have a special need, but I thought babies had to be at least three months to cruise? By three months I don't think you need to sterilize anymore, you can wash the nipples in hot water in the sink, just pack a little dish soap.
This is not meant as a flame, but IMHO any child who still needs sterilized bottles should maybe not be traveling on a cruise ship with 3000 people in close quarters, and visiting ports of call in third world countries.
Anne