Good suggestions here, If you can keep everithing dry (as in your Dryzone 200) I would be more worried about the heat than humidity, so keep the bag where you put your film always in shade.
About your 15 hour boat trip, Is it a large boat with cabin or a small open one? If it is a small open boat, assume that everything will get wet and will be exposed to strong heat.
Besides vaccines and bug dope, bring pills against diarrhea and vomit. Also quinine is recommended against malaria
Bugs will be the most annoying thing by far, especially one very small (smaller than mosquitoes) which I don't know the exact name in English or Portuguese. In Venezuela (where I live) they are called "Jején" and they can pass through regular mosquito nets. You'll need a very fine screen. Anyway ask the locals what would they recommend.
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