I'm quite happy with the way that the print came out. There was some slight warp on the bottom corners (hazard of printing in a freezing room with no enclosure) but the overhangs for the screw holes came out great.
The .stl for this file is available for free download here if you have a 3D printer and want to take a stab at this design.
If you don't have a 3D print but may have some use for this holder, you can purchase the holder here.
I recommend using Command Strips to mount the holder, though screws can be used to affix the holder as well.