This 3D is very helpful if your Child want to trail his trailer from i.E. Rolly Toys on his BERG Buddy car.
As better the material is as more resistance it will be against breaking... would be even better in PA! But if you want to use PLA, please use at least 8 boundry layers!
Just stick the coupling into the Seat Tube and fix it with a M8 screw with an selflock nut.
If you want to use the Seat at the far rear seat position, you have to cut out the seat a little, just push the seat on the M8 screw, you will recognice the mark, where you have to cut out...
PLEASE use MORE than at least 8 Boundry layers!
Because PLA is not weather resistance, please paint it to protect it for UV...