Friction. That is how my top, bottom, and side panels that flank my screen on my false wall work. Nice and snug, but still easy to remove. I just use the "goal post" frame to provide a solid stopping point vertically, and then added a couple of 2x2 strips to the side walls to keep the left and right panel in line with the screen.

No magnets. No velcro...

Farewell - June 4, 2020