I believe I started with 32" x 17" wide and then cut down to follow the contour of the Quarter panel.... there welded to the outside of the factory frame rail and the quarter panel wheel well lip was trimmed back 1/2" so I have a full 15 3/4".
Thanks, I am doing something similar. Now I just need to try to figure out how sturdy the quarter panel is after the tubs are installed. You are seam sealing it to the quarter, correct?