Magnetic Cover for Modular Tile System

While using the Modular Tile System (https://www.thingiverse.com/thing:2402641), I noticed that when I carried the larger tray with smaller trays inside of it, they tended to shift around and felt like they were going to fall out at any moment. So, I created a cover that goes over the top of the large tray while all the small trays are stored inside, and attaches magnetically to the large tray.

The magnets are strong enough that you can hold the entire thing by the cover itself, though if you shake it, it will come loose. Also, be careful when you add the magnets; because it's a cover, the polarization may be opposite what you think. The best thing to do is use the large tray to test each side.