As for mounting electrical and electronic controls and devices in holes in 3/8" or 1/2" plastic, THAT IS INSANE.
I have made many, many custom electronic control panels and can tell you that almost NO electric or electronic controls or other devices are made to mount in a panel that is that thick. Generally speaking, from a lot of experience, the range of panel thickness that the parts are made to mount in is 1/16" or LESS. The thickest panels that I have made were 3/16" but I often had to either mill that thickness down on the rear or use thinner plates fastened over a larger hole to mount many parts. Even then, adding one or more stiffeners on the back of a thinner panel is better than using a thicker one.
The general way that electric and electronic enclosures are made is with a front panel that is 1/8" thick or THINNER. In my opinion, after decades of practical experience, 0.050" aluminum is the maximum thickness that is practical for such construction. Only when the panel is very large would I consider using thicker material. And chassis punches are the ideal way to create the odd shaped holes.
But many electric and electronic components have a built in bezel on the outside of their mounting section. This bezel can cover parts of the openings that are not strictly necessary. So a small milling cutter, like 1/8", can be used to make openings for a variety of parts that have odd shaped openings. Here's some examples:
Double D Fuse Holder
D Shaped Hole
Rectangular Hole
D Sub-miniature Connector
In the case of the D Sub-miniature connector, the second, alternative cutout is something that I have seen on some expensive, high end, professional equipment. A punch of that shape was used by a major manufacturer as an alternative to a more expensive one with the "proper" shape and the three holes. I have one of those proper, three hole punches and new, it cost over $200. Of course, I got it for a song on E-bay.
As far as I know, no one makes either punches or other tooling for cutting these odd holes in 3/8" or 1/2" panels, even if those panels are plastic. Milling would be the only way and you would have to mill a well on the rear for the actual body of the part to fit in while it is supported by only the front 1/16" or less of that plastic. That is going to be a more expensive way to do it.