I printed the tractor an wheels from the tractor Model in the “Original model” section. You will need 4 additional of the small wheels for the trailer (same as the front wheel for the tractor).
The original model doesn't have the wheels as individual models, but I just removed the unnecessary extra wheel in the slicer.
The wheels were a little tough to get on the tractor, but I found that warming the part up a bit made it pliable enough to get them on easily. I did this in a dehydrator, but you could also use your print bed (put an upside down bowl or something over the part)
The author remixed this model.