Recreational & Family - Advent Allycat Hitch Problems

I bought a used Allycat trail-a-bike. Unfortunately, the hitch seems to be made for a seatpost of some un-godly small size less than 1".

It uses a top and bottom collar that holds the hitch mechanism in place on the seatpost. I installed 1 collar and used an old inner tube to keep it snug. But this doesn't last long before it comes loose.

Is there any place that sells just the seatpost hitch? I'm will to try another vendor to see if I can salvage this trailer. I've seen Traileron but I don't know if that's sufficient to hold a trail-a-bike.

Suggestions?

I have one also. Using one collar is not tight enough? Have you tried using both collars?

Sorry, I wasn't clear. When trying to use both collars the inside diameter is WAY smaller than my 27.2mm seatpost. In fact, it looks smaller than 25.4, if that makes any sense. As a result, the outside diameter becomes so stretched that the hitch won't fit over it. I can't pry open the hitch big enough.

My kludge was to only use one collar but that's not stable.

Pull the seatpost out of the frame. There should be a number with the symbol ø followed by a number. That is the seatpost diameter in millimeters. If you need to shim down the insert, cut an aluminum drink can.