Was not able to completely remove my liner as it is quite the PIA to accomplish alone. Was able to see far enough to notice little holes in the four corner areas where a D-ring or similar could be attached. They were not recessed, basically flush mounted in the groves, not on tops.

Doesn't clear anything up, just a note...

 

i just went to the junk yard and took the 2 tie down hooks fromthe back of the bed and welded then to the front about 2 inches from the bottom of the bed. they work great.