I liked Stivos design, but I was looking for something to mount on my tilted window sill.

So i remixed it.

The insert is now 2 parts, the top (with the big hole) can be glued to the outer shell with a couple of small dabs of glue, the bottom insert can be mounted to whatever surface you like. To screw it down I added 4 4mm holes.

For overhead mounting the insert can be locked in place by adding two 4mm screws to the holes in the short sides.