Print off hinges and clips (I use 6 hinges and 4 clips, 2 clips and hinges for front and 2 hinges and 1 clip for each side, see photos)
Cut out 3mm acrylic to shape. (It would be great if someone could attach a lasercut window thing to this)
Each clip and hinge needs a small cutout from the window for it to fit snugly.
Hinges are designed around 3mm steel bar (M3 bolts would also work).
Install and you are done.
I have included the .dwg file for anyone that wants to change it.

edit: Drandolph has made a cut file for the windows; thingiverse.com/thing:30894.