I normally publish and update all my models at MakerWorld. They are only here on Printables to keep the accounts consistent.

Please download the newest version here at MakerWorld.

Best printed upside down with 3 walls and 100% infill to get it very strong. PLA works fine.

No support needed.

Attach it to the wall with double-sided adhesive tape. 

Update 2024-01-10: I added a version with closed sides.