I concur with earlier post on military surplus. Both Willys and Bantam used military tubs and frames and sold trailers under the SPEN and Bantam names. Some trailers were marketed through Sears stores. The military trailers would have the lunette eye and would be connected to a military pintle hitch. The civilian models would have a bolted on Fulton coupler in a under 2" ball size, something like 1 7/8'" The SPEN and Bantam trailers are very popular with the early jeep CJ collectors. The jeeps would have a simple bent plate and ball attached directly to the rear crossmembers.
My current military staff car project would never be expected to tow a trailer, but with the gravel and stone guard and the distance from the rear bumper to the nearest weight bearing cross member would be prohibitive, IMO. So I would look at some sort of direct bumper mount.
I don't hink many trailers were used in the civlian marketplace in that time frame and lead to the creation of the station wagon, panel truck and eventually, the SUV. If you needed to tow a trailer, presume it would involve a pick up truck with ball mounted directly into rear bumper as in modern pick up trucks.
I have several of the lunette eye shafts where the eye loop has been cut off and a Fulton coupler welded on to use a military trailer, casting, landing leg and safety chains on a modern ball. Good 'ol Bubba.
Super AC too.
