A newer, improved version of the adjustable width trash bag slider.

Now the rail sliders are already attached to the holder pieces, and there is a little nook at the lower side of them to avoid collisions when multiple such holders are attached above one another.

Printing: 0.2mm layers, lay down the side holders on their respective outside face. 

The slider will need a tiny bit of support below it as it does not extend all the way to the outside face. PrusaSlicer's auto paint supports feature will work perfectly.