You should be able to use small toggle bolts or wall anchors, which have little wings that grab the back of the surface. Take the brackets and ask for the right size at your local hardware store.
Great advice Steve! He is absolutely correct, Home Depot & hardware stores sell them, just tell them what it is for. If you do not use the proper anchors it will come out of the door, especially due to the movement. Also, you will need to pre-drill a pilot hole with a smaller size drill bit that is made for metal (also sold at the above stores). Good luck with the project, you can do it if I can!!!LOL
thanks Lee Ann.....
magnetic brackets ,they do sell them.or just buy strong magnets and rig your own
They also have magnet rods that stick out a little bit if fab is to heavy add more
They sell heavy-duty magnetic curtain rods/towel bars. Don't get the cheapest type. No need to tweak them or add more magnets, which is cheaper in the long run.