Sod it, decided not to procrastinate and just do it now for you. Not that I wanted to put off cleaning and taking the trash out or anything ...   Here goes:   Length:275mm Width: 57mm Material: Any cardboard but I advise a thicker piece so it has some rigidity.   This size piece should fit nicely in the gap between the motherboard and the fans. The drive cage presses slightly on top of the piece keeping it in place. That being said I also added a small piece of tape on each side j