Not that it matters now, but I mounted my stereo in the glove box many years back (when I had a stereo). I simply removed the glove box insert, scribed an even line all the way around the plastic glove box insert opening (where the insert seals against the dash opening) about 2" deep, then drilled a hole 1" deeper so I could trim the 2" deep insert opening with sheet metal snips. The rest of the glove box insert was discarded since I only needed the opening that fit the dash. I fabbed a piece of aluminum sheet with the glove box dash opening marked out on the aluminum, and some "ears" around the perimeter so I could rivet the 2" section of glove box insert to the aluminum.
The polished aluminum is what the stereo is mounted through, and the entire setup is supported by sheet metal "C"shaped channel that leads to the grab handle studs on the front (trunk) side, and the lower wiring cover mounting stud. Don't mind the missing stereo face trim or the vinyl loosely placed in the photo around the opening (I JUST installed everything to test fit it and took a photo). I stitched a narrow length of foam backed vinyl to hide the pop rivet heads and I was just checking the length of the vinyl before the final stitching and gluing took place.
Just throwing my method out there in case you need another idea. You could fasten or glue the plexiglass over the top of the aluminum. The stereo was mounted very rigidly and never moved or rattled.
Andy