Though I completely built the model from scratch it is based off of the Retropie Console found here: https://www.thingiverse.com/thing:2469580
I had originally printed that console to use for my Retrobox but found that it was not tall enough for the LED Arcade buttons I used. At that point I went ahead and modeled my own version in Fusion 360 changing and adding what I wanted in my Retrobox.
There are already risers built in at the bottom with holes to use to secure the pi as well as the arcade joystick control module. A hole was added at the back so that the USB cable can come out and connect to the pi from the back. This was done so that you can also pull the cord out and connect it to another Retrobox to use as a second controller.
Hex indents were added to hold a hex bolt on the inside to secure the top to the bottom. I used machine screws for this as well as to secure the joystick.
Arcade Joystick and Buttons Used: https://www.amazon.ca/gp/product/B01M2X88QP/ref=oh_aui_detailpage_o08_s00?ie=UTF8&psc=1
I did put some manual supports on the open squares at the back and side of the bottom to prevent sagging but no other supports are required.