sorry, haven't been on here in a while, the sides and boxes are 1/8" mild steel, the floor is 3/16", fuel tank is 1/8", it is recessed 8" into the bed, the headache rack is also 1/8" and is made of 42 different pieces of flat plate, the main rails are 2x3 1/4" wall tube, the crossmembers are 1/8" 3 inch tall formed channels and the gooseneck hitch and mounting brackets are all made of 3/8" with it being doubled directly under the gooseneck ball... the truck's gotten a little scratched up at work lately, 22,000 miles in 6 months, it works hard and does its job very well, i wouldnt change a thing!... ... ... .