I'm using these 3 inch square HD inside corner brackets (scaled at 75%) to frame out a double tall printer enclosure for two (2) more MK3S+ printers. The ones I've printed in the photo are with a .6mm nozzle at .4mm layer height on draft. I had to  scale down to 75% of model size because of print time and they still worked really well with 1" drywall screws. Check out the picture for how I used them. I've also got a HD inside edge bracket for your not corner intersections. I'll keep adding files as I make them.