The piece of cardboard in the pics below, would be a steel plate, welded in place, with a 1" in diameter piece of steel, maybe 1" long, welded onto the bottom of the plate, there would be a hole through the plate and the steel below the plate, which would accept a removable stud that would have the hitch on it. This would make it removable so I could use the rack, without the trailer, and it would allow me to raise the mounting point to the existing height I am using now, so I don't have to do major surgery on the trailer again.

In this pic the mounting plate would be directly above the rear axle.

In the second option, the mounting point would be forward of the rear axle, very much the same as the set up I have now with the Cannondale.
I think I'll go for the forward mounting position, as the handling of the trailer now is fine, good in fact.

This is kind of what I'm thinking about for a removable stud, it would have to be very solid and maybe one hole is not enough, maybe I'd make it with three holes and somewhat gusseted?
Comments?
Cheers!