Howard 350 certainly had a trailer made by James and Stone who were boat builders in Kent so may be the Bantam used the same trailer . Strange coupling though it fits onto the plough hitch,and utilises a hitch block so the trailer can pivot and has a swan neck to come over the rotors . This in effect tilts the machine forward so the rotots clear the ground . Rather in the same manner as if you were walking the machine to a site
I have been after one for years They are about and yes they were marketed as a howard accessory certainly for the 300/350 range