I have had a go at working with aluminium for the first time. Working out quite well.. Right now I have three ribs mostly completed. Two inner ribs with a relief in the corners and one without the relief which will be on the of the ends for the tank. The relief is not cut in the ends as the corners will get welded.
Last thing to do is final sand the edges and then drill/cut the lightening holes with a flanging to finish. Then it will be onto the tank skin.