I need to make two edge flanges to use for riveted lap joints on the following tray:

None of the demonstrated methods (in training videos) provide a working solution for the compound edge joints where the 45° sides of the tray meet at the end. The flanges created end up at odd angles and or overlap the material on the opposite sides of the joint, and do not account for the need for the edge flange to have angled "sides" so the tray can be cut from a flat pattern. The lap joint flanges do not need to "seal" the joint. The tray is aluminum, and our sheet metal fab vendor does not have ability to weld the corner joints. Any help appreciated.

Randy