especially when you are painting it on the inside walls of a 73 Dodge Van before insulating and paneling. Same "event" also involved my uncle scratching his head while I cut a hole in the roof for a vent:)
The one section behind the drivers seat "just never got paneled" because it was a strange, compound curved area. The contact cement alone held that R13 vertical and well attached for years. We had just stuck the bare glass side against the tacky cement, and it adhered well. If white glue works, it would be much less fun, but safer for attaching the R13 to the walls.
Depending on the enclosure size, sometimes you would be surprised at how well the glass will remain in place just stuffed in there against a wall.
The bottom piece never can shift, unless you turn the speaker upside down. The rear wall piece of glass, if fitted snug side to side, stays in place also. The one side wall panel of glass will also stay in place, if sized right. My glass panels are spaced away from the walls by 1x2's glued to the walls as needed.
YMMV, you can always staple or glue later if getting it to stay by itself does not work out. Sam
long sleeve shirt, latex gloves, and big ass shears help a lot. the more carefully you peel away the unwanted paper from the glass, the better it "stays together" for stuffing into place later.