Did you go with 1/4" material for the floor? Plug welding is very labor intensive on that size material. We used to plug weld concrete deck with 1/8" 6011 and the welding machine turned all the way up. no drilling. Just push the rod in and pull it out. if i have done one of those deck welds, then i have done a couple hundred thousand. some companies used jet rods (huge black 5/32 7022s) but those didn't work as well in my opinion. but concrete deck doesn't see the movement that the bed of that truck is going to see. did you stitch weld the the deck to the floor support as well? I am getting ready to redo the bed of my grapple truck as well in january. I am thinking 3x6 thin wall tube for the side and top plate and 3x3 thin wall tube for the wall support 11 gage sides and 1/4" floors with the floor being channel on 2' centers