My trailer is on and off daily so I wanted something quick and simple. I went to the hardware store and got a pneumatic hose coupling and a few feet of hose. Got the female fitting into the hose and secured with a hose clamp. Then bolted that into the hollow arm on my cargo trailer.

I was stumped about the male end and tried a few different combinations with flat bar stock that worked just ok. Basically bend it in a square U and put a hole in the end for the male coupling and on both sides to put the skewer through. It's a copy of the Bike Friday/BicycleR Evolution hitch and I couldn't get it to work correctly (not much access to power tools). So I just ordered that section from Bike Friday and it works perfectly.

I'm very proud of it as it's very professional looking, very secure, and very easy to use. I haven't been on a long ride with really heavy cargo yet so I'm a bit worried that the hose might rip out of the arm but so far it's carried moderate loads fine.