My rack/milk crate on rear of my tw has been upgraded to a all aluminum basket.
It seems to be really made well with all joints tig welded - I got it off eBay and is actually made for a Rambo e-bike.
I figured that would work well on the TW
They make 2 different sizes as well as a gun rack that could also be easily adapted to our little tw-the rack I mounted is the large one-the small basket is the size dimensions of a milk crate.
I will note also the platform the basket is mounted to is a cheap flat rack fit all motorcycle rear rack that came from eBay as well-now the trick will be not to overload it with to much gear!
Maybe I will consider the small one when my present milk crate succumbs to sun degradation. You will have to be careful to not overload it as the welds on the frame section under the rack have been known to break under too much load.
I used to have an old ammo box attached to the back of my TW. It was useful but I was worried if I wiped out that box would get me in the back so I took it off. At least the aluminum basket has rounded corners.