When things fall apart it gives me an opportunity to contemplate how they were put together. I can see how the ribbon was attached and how much of the case I need to cover. This box was a cross between a cigar box and a clamshell, but easier to teach than either.
I've already started printing on the Pantone postcards in preparation for creating a unique book with them. I knew I wanted to put them in a box, so why not reference their original container?
It's a nice clean, quick box. You build a four-sided tray. You make the case. Here, I've added a piece of museum board to make a relief image on the cover and stripped out some recesses for title strips to add later. I use a brass spacing bar that is three board thicknesses to help with the measurement between the case boards.
You make a slit in the side for the ribbon that will help lift the book out of the box. Thread the ribbon through and glue it down. Add a strip of self-adhesive linen tape to secure it. You don't have to wrap the outside of the left edge of the tray.
Glue the endpaper across the joint of the case and line the tray. Glue the tray to the case.
Then glue the side to the spine.
And there it is.
More detailed boxmaking instructions may be found in Making Handmade Books: 100+ Bindings, Structures & Forms.