What size is it? We have a 23' Zodiac and it has/had to go through all the registration procedures as with any other vessel.
The rest of your post is very confusing. Mulege is on the Pacific side, we are on the Caribbean. AK is short for Alaska.
For boats entering Belize by water you check in and then when you check out you are charged a fee depending on how many days you have been in the waters of Belize.
I don't know the deal if you trailer in but you can be sure that they will have a way of nabbing you for customs on the way out if you don't have that boat with you. It won't be the value you tell them either it will be the highest price they can find on the Internet.
Thank you for your input, SimonB. I meant to put AC (short for Ambergrise Caye) The phonetic part of my mind must be misfiring. My inflatable is made by Mercury actually, but it is near 16'. Sure Mulege is on the peninsula but I could ferry across to the mainland from La Paz and drive on down.
I wanted the freedom and reduced expense of using my own boat around the caye for a few months but I am shelving that idea. Better to be shown around and get the benefit of the local knowledge. I think that I will instead fly in and experience things without the extra baggage. Then consider bringing my RV and boat/trailer if it makes sense another time.