I used a vanity mirror clip at the bottom of my monitor lexan. You see these at the bottom of most bathroom mirrors, the metal strip that runs across. It came in a 6 foot length, so I just cut it down. I still need to paint it, right now it's bare aluminum. So that holds the mirror from the bottom.
For the top, I got some window screen clips, and screwed 3 of them into a strip of 1x1 across the back edge of the speaker panel, where the top of the lexan meets. This way I just swing them down to secure the lexan, or flip them up to remove the glass for cleaning. Super easy!