Ingenious construction - making 8 corners rather than 6 faces. I joined them using this method instead of sewing. I also put some plastic canvas inside to help keep the shape when stuffed.

As this is a weighted companion cube (and will be used as a doorstop) I added a tub of ceramic baking beans (inside an old pair of socks) when stuffing.

Looks pretty good! Bit wonky in places, but still ok.