The IFFHS ranking system is crap, although a few simple modifications (like correcting for the fact that different leagues play different amounts of games!) could make it a little better. Its advantage is that it can be calculated with a minimal amount of data.
The difficulty in the caribbean is that it's hard to calculate the relative strengths of the leagues because participation in in the champions cup isn't that extensive. Maybe you could also take national team results into account as a reflection of domestic league strength.
I played around with a CONCACAF clubs ranking a few years ago (it was on BS pre-crash) and it came out pretty well, but when I tried to update it the next year all the league ratings were screwed up because Olimpia beat Pachuca 4-0. Maybe a more clever scheme than mine could get around that problem.
Basically my idea was to first rate all the teams in a league relative to each other (nothing complicated, just used average goal differential per game). Then I used Champions Cup results to get league ratings. Because each country got two teams in the Champions Cup, I set the average rating of the top two teams in each league equal to the league rating, and then everyone else's rating was just set relative to the top two teams. This did a pretty good job of dealing with leagues where there were a couple of top teams, but not much depth.