To be honest, I don’t want to be following you down the road with a home-made trailer assembled with wood, screws and glue. I think the logical starting point here is a small, inexpensive steel utility trailer that is modified by adding a padded cradle for the boat. This will give you a welded steel frame, suspension, lights and will meke me feel much safer behind you on the way to the fishin hole. All attachments for the cradle should be bolted through the frame with lock nuts. Keep in mind, you still need to license this contraption to use it on the roads. This could mean an inspection, especially if you don’t start from a fabricated steel trailer.