A very simple (if over-engineered :) bracket designed to hold a right-angle in a piece of corrugated cardboard 6mm (nominally ¼"). The bracket has holes to optionally push brads (small nails) through to help hold the cardboard in place.
Print 2 brackets for each corner, one each for top and bottom. Create the corner in the cardboard by scoring the cardboard sheet with a knife (i.e., do not cut all the way through), then bend along the score and push the brackets on.
With reasonable print settings, 2 brackets can be printed in just under an hour.
I do not do prints that require a printer enclosure, but my Prusa is in the basement and definitely could benefit from a draft shield. I used 6 brackets and the box my Prusa came in to create one and it really helps!
The author hasn't provided the model origin yet.