Importing in Grenada will make you subject of paying taxes
at about 50% (look on the government
website, there is a page somewhere to calculate). The only way to avoid taxes
is that it's written 'boat in transit' in the pack you have to receive, with the references
of the boat, and that you are all cleared with the customs.
In Trinidad if you want to send regular stuff from the US you need a skybox or someone receiving for you, you have to check with the customs because a lot of stuff are illegal to be imported, and the taxes are at about 55%, and for some specific stuff you need to apply to an importing licence (1 year delay). Importing new stuff or boat parts
through local businesses is easy though.
By the way, if you bought your boat in Grenada, the inbound is probably not in your name, be sure to be get all the information from the customs as you might have to pay taxes for the boat transaction if you stay in the country xx days after signing the bill of sale
and that you can still receive your stuff avoiding taxes.