Already ordered all the "stuff". Stainless button head bolts for the heavy duty tie down points. Planning on putting a hardwood plank beneath the bed for the bolts to go through.
The plank will extend perpendicular to the 2x8s, across the underside of the bed. Bolts will go through the recessed hold down, the 2x8 and the hardwood plank. Only 1/4' bolts, but 4 per hold down...Fender washers and nylon locknuts.
I also got a bunch of single hole tie downs to mount on the uprights for bungees and such.
Again, all stainless tie downs and bolts.
I'll send a pic when I git-er-dun.
https://www.ebay.com/itm/232241609909?var=531462564260