Saddle bag/rear dynamo light holder for bicycles

Print in PETG or stronger (ASA, Polycarbonate). Use 4 zipties to attach the holder to your saddle rails (the upper ones through the cutouts in the support rib, and the lower ones around the rail attachment and through the triangle so it does not slip off. You can use the two D-shaped cutouts  or the slit between them to pull the straps of your saddle bag through (or you can install the saddle bag as usual). Bolt a dynamo taillight to the attachment points (fits a light with 50mm bolt distance).

This should provide a very visible location for your taillight and hopefully keep you safe. And also keep your saddle bag higher and in a more aerodynamic position.