Terry,
Haven't done the trip myself - I think the route you describe is called the "thorny path"; found a website that may be helpful for you:
Thorny Path
I have been to Puerto Rico and highly recommend a stop at San Juan - there's lots to see and do for the family; if you time it right you will be there for one of the many street parties/festivals. Don't know what duties you would have to pay, but the rum is very inexpensive. Have fun.
Kevin