Just a thought; If magnets you find at big box stores don't cut it, you could try a 1 neodymium magnet. If they cannot hold, then I don't know what would. You can buy online in almost any size.
When I added a panel I(made of painted MDO board) to the inside of my metal stand to mount equipment to, I inlayed one 1"x1" magnet to each corner of the panel. I did this because I wanted a way to secure the panel to the stand with even equipment mounted, but not drill any holes. It kept it a "clean install", and, that panel isn't moving unless I want it to.