"Any idea how well a US based plan would serve me in the Caribbean? (if at all...)"
Great, if the plan provides "out of plan" coverage. (Ka-ching!)
No coverage at all, for the vast majority of plans, until a steep deductible is reached. If you look for a "major medical" plan as opposed to comprehensive health insurance, things become more reasonable again. Only because you don't have coverage for the routine little things, regular meds, and so on, until a higher dollar point is reached to begin with.
You might also want to look into medevac insurance, since Miami-Jackson's Ryder Trauma Center is apparently the only Class1 trauma center available between the US and the interior of South America. (!)