You know what thingiverse really needed? That's right, another soap dish. I couldn't find one that was quite what I wanted, so I made exactly the right thing.
This is intended to mount to a shower wall using suction cups. The design allows you to customize the suction cup keyholes for whatever size suction cups you have on hand. It also allows you to flip them & and add a 3rd if you want the shelf at the top rather than the bottom.
I made a slight modification to this part. There was a tiny imperfection half way back on the outer rim because it wasn't totally flat. This new revision fixes that, flattening out the top of the rim. See Changes.