I'm no metalsmith, and not much of a mechanic. If I need a part for the motorcycle, I first turn to wood. Not so good for engine parts.
I made the box to sit on the back a few years ago. I recently decided to make a luggage rack to sit on the curved top of the box. Here are a few pictures. I have not yet decided how to keep it in place. Maybe bungee cords, but I hope to come up with something more interesting. I want it to be easily removable. The box, by the way, is mounted on a black, steel luggage rack. I have a small piece of wood under the seat. On it are mounted a fuse block and a relay for the dual car horns I added a few years ago.