Along with items stated above, get a bill of sale. Have the sales price broken into the three items, boat motor and trailer. Three different registrations so they need to have the price of each not just a total for all three. It's a simple process
When I did it, everything you'll need was in the paperwork you get from TPW, the seller can fill in how the total amount paid is broken down.. For example, if you paid 3,000.00 total, you can break it down on the paperwork as 1,000.00 for the boat, 1000.00 for the motor & 1000.00 for the trailer.