So if you've read this far and still think you want to do this, there's some things that you have to purchase, and there's just no getting around it.
First, if your trailer is aluminum, stop. They flex too much, fishtail, and will break. They are built to be lightweight so you can pull it easier while peddling a bicycle. Your trailer must be made of steel. The Zero won't be able to tell the difference, although your legs would if you were peddling.
Second, the steel trailer must have the option for the attachment arm to be on the right hand side of the trailer. I forgot this detail when buying the second trailer, and had to drill out rivets and swap the bracket and arm from trailer 1 to trailer 2, since the arm that came with trailer 2 wouldn't work without major modifications and there wasn't a bracket at all on the other side.
Third, you will need to grind off the outer flailed lip of the main axle nut on your Zero. You'll need the extra threads it exposes. Just square it off so there's no flair. Then put it back on the axle and torque it back down.
Fourth, you'll need to widen the hole of the mounting piece that fits over the axle. Grind it out with a drill and some sort of grinding bit and make it as circular as possible. Take your time, it took me about a couple of hours with a cordless hand drill. It'd probably be much faster with a drill press.
Fifth, go to Fastenal
https://www.fastenal.com, and order a M20-1.5 Hexjamnut ZP Part: MJ2760000ZP0000. The threads will match perfectly. This goes on the outside of the trailer mounting bracket, and probably won't fit all the way on. Try to get it at least 2/3 on. You'll probably want to use blue loctite, although I didn't.
More details later.