If that's a trailer it seems a bit silly. Why not use the wheels of the model car as the wheels of the trailer. Trailers have been built to work that way before. But I really prefer the trailers made from the rear part of a real car.
This sort of thing http://www.flickr.com/photos/31221270@N07/2926159090/
This sort of thing http://www.flickr.com/photos/31221270@N07/2926159090/