EDIT: Evomade just published the Viewbox cardboard QR code. Here it is!
First off, unfold the goggles, and get them bent into shape at least once.
Heat up the hot glue gun. The plastic that the frame is made of, both sticks to hot glue, and is not damaged by it. So if you screw up.. you can do it again after peeling it off.
First, glue the nose bridge bits to the top of the goggles. Do so by running a bead of hot glue along each side of the nose bridge peice. I also ran beads of glue along the outside corners.
Here's a view from the other side. I also spread open the nose peice, and squirted some hot glue in there. You can see it squeezed out a little.
Once the bridge peice is solid, make sure the lens frame is clipped into the frame, and run beads of glue to hold the lens frame in place.
And here's what they should look like. Here they are without a camera in them.
And here's a complete viewbox. Without gluing, they really don't want to hold their shape.
Finally, I used some superglue to hold the trigger magnet on my viewbox.
PS: The foam bit, and micro velcro strip, are there to cover up the camera window for use with small phones.