Heres what I did. The tie downs are simple D rings with 2 bolt holder. For the rear which is steel I drilled and bolted the rings through with washers and lock nuts. The back is easily accessed by taking out the taillight (2 or 3 screws where tailgate meets the bed and it pops out) For the fronts I took 1ft of 3" 1/8" thick flat stock steel (available at most welding supply stores), bent it 3" from end in vise using a small sledge hammer to almost 90 degrees. I lined up the tiedowns on the bottom inline with the drain hole and drilled the bed hole. I lined up the steel underneath and had an assistant mark the holes on the steel. I took the steel back out and drilled one hole. Then bolted it in place with the one bolt and then lined up and drilled the other holes. Used cutting oil to reduce heat transferred to bed. Side holes were easy to drill after the bottom was bolted in. I just made sure the steel fit well to the bed shape before any drilling. I also drilled the steel blocking the drain holes next to the tie downs.
I hooked my ratchet ties downs and cranked them tight and did not see any signs of stress so they should hold any reasonable loads. The only issue have is the tie downs are not spring loaded and they rattle. I use a couple of bungee cords to keep tension to prevent rattling and the bed mat covers the floor tie downs.
Tie Downs $3 ea x6= $18
steel $2.50/ft x2'=$5
Grade 8 bolts, lock nuts, washers $5
Total $28+tax and 1 hour to install