2 pipes that you add to the top that go from the top to the ground (on the side of the trailer) on a 45 degree angle. You slide the boat up them using them for a "ramp". Then after loaded, you remove them and fasten them to the trailer floor.
Better yet sell that trailer and buy yourself an enclosed trailer. We tow a 10 footer carrying two motorcycles, an air compressor, a tool cart with tools, lawn chairs, tables, rugs and everything else under the sun. We don't even use the roof. I could stick a boat up there if I wanted to. It's nice to have a garage and I can lock everything up.