Step 1 : Glue the deep bags
Step 2 : Attach the front panel sheet with the two holes
Step 4 : Attach the Back panel
The back panel fit like a charm.
Finally I threw it all together. The mockup is finished. Sure, there are many many things to improve, but this is a good start.
I want to collect at least ten interested people. If that happens I collect offers for that little friends and start this project. Anyone?