I posted this on another Forum, but I thought I would post it here as well. This is my how too for magnetizing Movement Trays.
Once the tray is made, I then cut to size the sheets I use to line the trays. For my trays I use a product called Flex-Steel (I think? I cant find the labels anymore lol). It is not magnetic itself, but is ferrous enough that anything magnetic will stick to it. Its self-adhesive peel and stick so makes the process a lot easier.
Cut it to the inner size of the tray.
I like to align it to the front rail of the tray and then slowly work it down so that there are no air bubbles. Use another piece of plastic to help squeeze the sheet to the floor of the tray to make sure it has adhered thoroughly.