Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:3534450.

I added built-in supports to the body as printing a rounded bridge causes printing issues. No added supports are required. Simply use a pair of needle-nose pliers to break away the support to allow the rubber band to pass through the body.

In Prusa Slic3r, under Printer Settings | Layers and Perimeters | check "Detect Thin Walls".

In Cura slicer, under Printer Settings | Shell | check "Print Thin Walls".