Here are five seaplane airports in the caribbean from Trinidad up to Martinique. Each airport has a water runway and some parking spots if you want a cold and dark startup. I placed the runways not to close to the islands, so there shouldn't be any problems with larger seaplanes. These are complete fictional airports and were mainly created for a "Flight Sim Break" group flight. 
We are flying (almost) every Saturday, if interested, join us on  our Discord.