the old third wheel boat trailer design hunt

Does anyone know where I could get plans or ideas for a drop down spare wheel holder for a boat trailer? I want to have the spare mounted on a hub that can swivel down at the front of the boat trailer to make launching and retrieving easier across a beach. Would appreciate some pictures or designs if someone is willing to hand them over. I've priced just the swivel plate and axle without the hub and it came in around $200. Surely should be able to weld something together cheaper than that.
Look forward to hearing from you've

Ps I currently have a standard Dunbar trailer for my 5 mtr trail craft and am looking into taking up north. Should I replace the standard tow hitch with a treg hitch and add extra heavy duty leave springs and springs?? Any advice anyone has on this would be appreciated
Dave