52 years ago, my Dad helped me build a trailer for my Bicycle, to haul outboard motor, 2½ gallons of Gasoline, fishing poles, 20' bait seine, 2 float cushion life preservers, and small toolbox. I pulled that thing for 3 years, 10 miles each way, to where I kept my boat.
We(he), took a tricycle piece broken off the headpost, turned it upside down, and inserted a piece of Galv. Water pipe. It fit well, so, he went to a tree that had a crotch from 3 trunks, and slowly bent that pipe into a "Gooseneck" design. When installed into the tricycle piece, that at level with the ground, and the gooseneck was hammered flat, and we put a 2 piece clamp bracket under the seat, with a long bolt clamping the pieces to the "V" shaped framework. The bolt stuck up, so we damaged the threads and drove a nut down over the threads to lock the nut, put a washer on, put the gooseneck flat side over the bolt, and installed a washer and cotter pin.
There was a wooden box that I built and bolted to that tricycle frame, that sat between the 2 wheels of the tricycle, and I wish we had had a camera to take pictures. We were pretty poor.
So, that would be how I would put a trailer on a Bicycle, again.
Sorry for this long 1st post.
