^^^^This site has all the info.
You still need to buy a lic plate for the trailer but the boat is no charge. Those big numbers on the boat are just for identification, in case it's found floating across the lake with nobody aboard. If you buy a used boat, just take the number (already on boat), and register your name against it. If you get a new boat, simply fill out the form and the feds will send you a number. Get numbers made up add stick on boat.