I am in the process of building a new case for my new setup. Basically I am putting a piece of plexi as the top of my case and a piece as the bottom. The sides are going to be my storage bin:

Here is the bottom with a rough layout of how it will go:

The motherboard will be sorta like this (but with the top piece of plexi on it):

Stupid question I know but what can I use to sorta join the top and the bottom pieces while keeping them separated and sturdy. It's about 5.5".