Please take some time in the near future to check the U-bolts that secure your cargo box to the truck frame rails (see attached pics). Over time, these U-bolts will loosen, crack, break, or sometimes rust to the point of being ineffective.
It is a relatively easy fix at most any semi trailer repair shop or Capitol City Trailers if you find yourself near Columbus.
Please let me know if you have any questions or if you find any issues with your U-bolts so we can address the problem.
Thanks and drive safe,
Equipment Maintenance Manager