Topsider homes are excellent in this environment. They are really well engineered and super-durable.
The "issue" is all about importing them because they are made of wood. There is no representative in Belize. You'd need to buy stateside and ship the kit. Check with a custom's broker to see if they can get the kit into the country.
The Tree House on Ambergris Caye and Nautical Inn in Placencia are Topsiders - not sure who put them together or what special talents they needed to do so.