My metal bed frame was really bent up. I was sick of lumps in my mattress, so I made a plywood cover to have a flat surface for my mattress.
I got out a sheet of plywood and some tools.
I cut the plywood to size, and cut notches in the areas where my bed rail I made connects to the frame.
I then painted the bottom of it black, this is what shows through under the bed where my desk is.
It fits and works great.
You can see the bed rail going through the notch I cut.