I was looking back at the OP's post. A mention of a seatpost hitch.

That brought up the design by our local co-op.

The Hauler ? Human Powered Machines



Two unique things about their build. First the trailer has a built-in kickstand. I haven't actually pulled one so I don't know how they handle speed bumps or steep driveway transitions, but otherwise, the kickstand typically is just enough above the ground not to cause problems.

The other thing is that it has a very convenient handle at the hitch, so the trailer can be moved around without bending over.