I am certainly no expert, but since no one else has responded to your post, I'll give you my personal experience with mailing stuff to my beloved Belize. Between customs and duties, it really is expensive and iffy.
We sent a picture (worthless to anyone else but us) down to Ambergris Caye last year. We paid $35 for packing and $90 for Fed Ex (and that was 75% off for company discount). Now, this only guaranteed it thru Belize City.
Then...once when it got to Belize City (and Fed Ex washed it's hands of it), we paid $50 for a customs broker, $25 for duty and $10 to Tropic for the ride to San Pedro.
Soooo, you do the math...very, very expensive. Plus, we feel lucky to received it at all.
The moral of the story is...if you want to bring stuff to Belize, accompany it down on the airplane. Cheapest way to go...and YOU get to