Duplo Train Connetix (or Megagon) Coupler

My toddler is really into the Duplo Train set at the moment and worked out the trailer platforms of his magnetic tile sets have hooks that could be attached - the Connetix and Megagon sets have almost identical sized holes and fittings for their wheeled platforms. 

They don't quite fit securely though and the train will move and often leave the trailer behind so I built this coupler.