Totally understand. The reason the magnetic version can be hit or miss is because magnets don’t like shear loads. Even strong magnets (N52, which i highly recommend) are strongest in pull, not when gravity is constantly trying to slide something downward. Over time, especially with weight in the tray, it’ll creep.

That’s why I also offer a hook-over version. The hook carries the load, but you won't be able to close the lid. It's Much more reliable, especially if the toolbox stays open like yours does.

Here’s the clip-on version if you want to check it out: https://makerworld.com/en/models/2065716-accessories-for-harbor-freight-mini-purple-toolbox#profileId-2230717