Try this one - it draws solid geometry, and allows you to parameterise all the dimensions, including the cutout size. With a little bit more work, it even allows you to change the corner radius of the cutout hole - just add a corner_radius Size option for the corner piece, set in the parent, and applied to both the X and Z sizes of the corner pieces. and that will change the radius.
I’ve made four additional components - two sub-panels, and two corner pieces with the 8mm radius. I could have used just two, I realise as they are identical, but the right one is mirrored from the left.
edge opening example JWM.skp (377.0 KB)
I’ve left all the edges unhidden so you can see how it works. Hide all the ‘meeting edges’ where the components join, so it will look like one piece. But here’s a version with them all hidden.
edge opening example - edges hidden JWM.skp (381.9 KB)