I like the idea of using border towns with the DR for trade. Using a port city for export creates an artificial bottleneck for the export of goods which leads to excessive tariffs and loss of goods. I bet most Haitians would be better off exporting to the DR and then have the DR export some of the goods even though Dominican export points are by no means safe from exploitation.
What I've read about the trade in border towns is Haitians are taxed for the goods they bring in and if they do not sell them, they are taxed again when they leave the country. It seems to me they need an area which is neither Dominican or Haitian for trade to take place freely.