I built my own 8' by 8'6", 48" high chip box for my one ton dually. The truck wasn't a chassis cab originally so I had to build a 2"x3" sub frame and lower the gas tank two inches to fit the hydraulic hoist in. I have a cross bar across the top in the back so the sides can't bow out. I left the top open and built a fitted tarp out of 22oz poly impregnated nylon (think over the road truck tarp). This allows me to catch all the chips and still load logs/stump grindings with the tractor. It holds approx 8.5 yards so I added firestone airbags. I used 1/8" for the floor and 14 gauge on the back and sides. I used 4.1# 3" c-channel for the cross braces on 15" centers. For the side braces I used 2x2x1/8 tubing. I put a 1/8 angle rail around the top. It took about 3 days with one guy helping, including epoxy priming, and top coating the outside. I can post some pics if you want me to.