Just a simple clothes hanger for your door, 3 mm strong, several plates/versions:

• 16 mm / 18 mm / 20 mm (door width or depth)
• 3 or 5 hooks

Print in a strong filament! 

Feel free to scale in z direction (currently 1 cm, but you might get a non or less deforming hook with your filament at 15 or 20 mm z). Just make sure you deselect uniform scaling, so only z is changed.