Here the back of the shadowbox with the top covered with matboard is glued in place with wood glue.
Box face down
While the glue was drying, I moved the hanging hardware, putting two pieces on the long side and one on the short.
Then I gave the frame and the outside of the box two coats of paint.
Glued and clamped matboard on the long sides of the inside of the shadow box,
All that's left to do is put the glass back in the frame with silicon and add the hardware.