I usually try to avoid dispensing medical advice on these boards, but in this case I couldn't resist...
I am a board-certified pediatrician and see lots of boys (and girls) who wet the bed. In MOST cases, the problem runs in families and is caused by a small bladder capacity in a child who is a deep sleeper. As they get older (sometimes as late as 14-15 years of age), their bladder gets bigger, they become lighter sleepers, and they wet the bed less often.
Personally, for the cruise, I think your best approach would be a plastic mattress cover AND the super-absorbant chux pad. I doubt your 9 year old would like the idea of wearing a pull-up... but that is another option if he doesn't mind.
I would be careful about using medication. Two medications are often prescribed for bed-wetting (I do not use either of these). One is actually an anti-depression medicine which can effect the heart if the blood level becomes too high. The other is a hormone that causes water retention. This can make blood sodium go low, and I have seen kids have seizures because of it. In the end, you have to ask yourself, is the risk of potentially life-threatening side effects worth the elimination of the bed-wetting. Personally, I do not believe that they are.
The moisture alarms are great in theory, but in the real world what often happens is that the alarm wakes everyone up in the house EXCEPT the deep sleeper, who still wets the bed and keeps snoring even though the crazy thing is buzzing right next to his ear.
Let me also just mention... if you have a bed-wetter, definitely talk to your doctor about it. There are some other causes of bed wetting that are RARE but serious.
hope that helps...
and now I'll resume the role of normal citizen...
