The Caribbean has very extensive VHF coverage, even at lower altitudes, and particularly in San Juan airspace. The only thing I can think of is if you're doing, say, SJU to Curacao at low altitudes, which is a 400nm over-water segment. Something you may reconsider doing in a piston twin or Caravan, anyway.
And anyway you are not allowed to do legs of over 300 NMs in twin piston, and and be over 100 NMs from land in single in the Caribbean for hire.
As far as VHF coverage, I use to loose VHF below 1500 about 100 NM away from the facility, I had no other way to tell ATC I landed and close my flightplan then to use an HF or my cellphone/satphone.
My current company flies in the Caribbean and we follow this regs:
CLOSING A FLIGHT PLAN
(a) The PIC shall make a report of arrival either in person or by radio to the appropriate ATC facility at the earliest
possible moment after landing at the destination aerodrome, unless ATC automatically closes a flight plan.
(b) When a flight plan has been submitted for a portion of a flight, but not the arrival at destination, the PIC shall
close that flight plan en route with the appropriate ATC facility.
(c) When no ATC facility exists at the arrival aerodrome, the PIC shall contact the nearest ATC facility to close the
flight plan as soon as practicable after landing and by the quickest means available.
(d) When communication facilities at the arrival aerodrome are known to be inadequate and alternate
arrangements for the handling of arrival reports on the ground are not available, the following actions shall be
taken. Immediately prior to landing the aircraft shall, if practicable, transmit to the appropriate air traffic services
unit, a message comparable to an arrival report, where such a report is required. Normally this transmission
shall be made to the aeronautical station serving the air traffic services unit in charge of the flight information
region in which the aircraft is operated.
In many cases the only way is by HF