Here is a picture of mine on my 50' as above these are homemade. I used threaded inserts where possible so I don't have bolt heads or nuts on the inside of the bed. The entire assembly is held by one bolt in each of the stake pockets (factory) so easy to remove if needed.
https://www.flickr.com/photos/advance-design_parts_co/8129206162/in/set-72157631867396207
I don't recall seeing many kits available then maybe they are now?