I first made a template out of posterboard for the aluminum pan, and used that to cut it out of some .032 sheet. I then put some slight bends in it to conform to the stringer shape using my pan brake with a heavy shoe on the edge. I wanted a softer bend.. I left it a bit long because I wanted it to wrap around the brace tube in the back. Once the pan was done, I could easily set the angles for the mounting tabs on the longeron. I just used a piece of scrap, made a tongue on one end to slide under the lip and drilled holes in the middle so I could use it on the right and left. I clecoed the mounting tabs to the makeshift jig and tacked them in place. Once tacked, I finish welded them.
