Here is how I mounted the On/Off switch for the main power supply and also the emergency stop button. I wanted to make these both a part of the machine so I mounted one on the side and one on the back.
Here is the On/Off Switch mounted to the backside. I used some plastic epoxy to really attach it in place. It's not going anywhere, trust me.
Here is the emergency stop button. I mounted this on one of the sidewalls so I could easily hit it if something went wrong. Only had to use it 1 time so far!