I'm not popular with this response, but we do not travel without proper restraints for our children. We have done both eastern and western Caribbean itineraries and found vehicles with seatbelts in all ports. Some ports require more research than others (e.g. Roatan), but even in Mexico seatbelts can be found. You likely will not find LATCH bars in foreign ports, but that doesn't mean you can't install a car seat with the seatbelt.
I'm a volunteer car seat tech in Canada, and I work in health care. I don't want to find out what a trauma centre looks like when I'm on vacation and my child is ejected from a vehicle because of a collision. Yes, child restraints are a pain to use while on vacation, but the laws of physics don't change because you are in a different country. If we go to a beach, I either make arrangements for the seats to stay inside (Steve at Tropicante in Costa Maya was very accommodating), or arrange for transportation where the vehicle is with us for the day, so the seats stay in that vehicle. I tip the taxi drivers well and I've never had a problem with someone getting impatient while I install 2 seats.
We have visited Cozumel and while we walked around the downtown area, I definitely saw taxis with 3 point seatbelts and top tethers.
