I assume you have the basic information on hotel occupancy rates (e.g. Ambergris Caye has a 48.6% annual occupancy rate)?
There have been a few studies done, though I'm not sure I'd make book based on any of them.
My free eBook on Ambergris Caye, called San Pedro Cool, downloadable from www.belizefirst.com
, has a little information of the type you're looking for.