These handy boxes can be used for various storage ideas or for a small battery. These fix to the original rectifier/regulator hole on the outrigger with an angled flat bar that fixes to one of the holes for a rear rack. Comes with fixings.
 
They have been successfully tested for fitment on a series III TV, a Special and a DL/GP. To fit a series 1 or 2, you will need to alter the bend on the bracket.