Unless you’re planning on carrying it with you by the handle when you go fishing, I’m thinking that you could put a cam strap (like the one pictured) through the handle, loop it around your neck and tighten it up so it stays in place. 😃
You might not want to refer to your box as a Richardson Chest Box though, lest it be confused with the original. A Rube Goldberg chest box might be more descriptive.
Oh, by the way, your box looks like a nice place to keep a lot of flies in when you’re not on the stream fishing with them. 👍