All you need to square your belt is make 2 marks on a sheet of plywood ,chalk a line ,now screw one end of your belt to the line.then pull tight put a screw at the other end ,you can screw a 2x4 to the chalk line to butt the belt to.square off the first line and chalk a second line for the other belt .now you should be square ,now lay out your slats double check for squareness you will need spacers i between slats ..after you double check for squareness pre drill holes threw slats and belt counter sink in the slats .