I had a custom box built that opens from the front so I could fit it right under the light without impairing the visibility of the light. I also selected a length that would leave space for a spare tire carrier on the other end of the bumper.That gave me a little extra height. There is a cross support welded to the trailer frame with two additional short supports welded between that cross member and the square bumper, making four points of attachment for the bumper and is shown in one of the photos. There are also two pieces of angle iron welded to the rear surface of the bumper to provide support for the bumper box and the box is attached to them with tapping screws from the inside. The depth of the box is such that it does not stick out any further than my spare tire. The box carries an air compressor, X-chocks, water hoses and electrical cords and most of the weight is on top of the bumper as opposed to hanging off of it acting like a lever every time I hit a bump.
The cost of the box was less than what Northern Tool wanted for one of similar size and I was able to design it to meet my specific application.