ALL CAPS IS LIKE SHOUTING. I found the brackets on Amazon.
http://www.amazon.com/4SQUARE-Safety.../dp/B00JASCNEE
They are an improvement of most trailer box bumper brackets. The concern I'd have is how strong is the actual box? They are usually pretty flimsy and only good for storing the stinky slinky, not really meant to hold a bike rack or other heavy load. In addition, the violent jarring that happens at the tail end of the trailer can create forces that can cause failure of many bike racks or platforms that are designed for the end of an SUV or van that has shorter distances to the rear axle.