I use a center hitch but made pads that lock on the tow hook loops and supports the ends of the aluminum tool box a friend and I modified to use. I then run 1" ratchet straps from eyes in the pads around the box and to the top of the bumper. This locks everything tight and distributes some of the load to the tow hooks/bumper. I also used marker sticks on the corners to remind me it is out there.
Here is a
link to a posting I made on the project a couple of years ago. I have improved the pads for the tow hooks for easier removal and went to the retractable ratchet straps since the pictures were taken.