For the hitch on my GS I just bought a section of receiver tubing, http://www.humphreystrailerhitch.com/BIZyCart.ASP
, and welded U brackets underneath so that it sets on the sidecar frame. The U brackets take all of the lateral force and I use steel plates and shackle bolts to keep it on. Comes off real easy if I want to remove it.
I offset the tounge on my trailer so that both wheels track in the sidecar wheel tracks. I am like Claude and I do not like the trailer sticking out the left side of the rig.