the stiffnes is not an issue with box sections because you don't adjust the wheels harder than you can slapp the metal sideways with your palm,i tried just for fun to see how hard i could run these simple things and there were so much lines from the wheels that you would need filler to make it disapear,the bigger you build them the more complex bow you will need to make,this will take 400 millimeters wide metal wich means you can wheel 800mm stuff