Thanks for reply. My bed is entirely wood except for a 6 inch wide plate around the outside edge. I think my approach will be to install 3 angle iron crossmembers to the appropriate wood crossmember and then use the plated screws you mentioned to secure the planks from the underside of the deck. My bed is 8'by 10', but I think I will go ahead and reduce the width after it is mounted on the truck. I think it can be done fairly easily at this point before I plank it.
