I did. The kart owner has the template. They're done in .050 aluminum, hand bent on the sides, and finger brake bent in the rear, and polished. Upon installation, the edges are dollied over the frame, drilled and rivets set.
The tank is a reproduction of a five quart Chilton. They are increasingly rare, and without dings and dents, very rare. Both karts in the photo, (65 Rupp and 66 Bug) are sporting those tanks. They run about $450 each, although the guy fabricating them has ceased production.