Agree, looks like a boat cleat. And to the OP, if you are looking at those, they also make some that pop up, so they sit more flush until deployed. Might be an option as well if you're worried about things getting hung up on them when not in use.They look like standard dock anchors.
The prior owner installed them; so I'm not sure how they got behind the panels.....but they were in there good and worked pretty well. There are a few easy options for you as well such as bed stake hole tie downs. Bull Ring USA makes a couple products that you may be interested in: https://www.bullringusa.com/?year_i...=4298&post_type=product&action=vpf-ymm-search.Huh, that's not a bad idea; @Billy James when you installed those, do you just fish the hardware up from below on the inside of the box?
I'm debating something like that or L-Track; never installed either, learning as I go