Dog carrier bicycle trailer (for a medium/large dog) (Caversham RG4)

Hi. We cycle a lot and don't have a car. We are getting a mixed-breed (and partly German Shepherd) 6-month-old dog, which I assume will grow a lot. If anybody has a bicycle trailer for carrying medium/large dogs that they want to get rid of, we will be able to make good use of it. My schedule is pretty flexible, so I will probably be able to collect at your convenience, morning, afternoon or evening any day.