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For the drawbar, the advice given by mikegarrison is spot on. There is some variation among different trailer designs and setup. You want the trailer to be level. Make sure that you have at least 50 lbs of tongue weight and the trailer rides nicely.
If you can find the thread on the Chase Race hitch, I'm pretty sure that I posted what I was using for a ball mount with the AP2 version of the hitch and the Harbor Freight trailer with 12" wheels.
While I was at it, I snapped some pics of my newly constructed trailer...
This is going to be my solution to securing the tires. The tires will be stacked two high, face to face, and strapped together and down to the trailer.
The drawbar I used was a 3/4" shank, 2" drop (or rise in my case), 1.25" by 1.25" receiver