After the mild steel plate I had used to insulate the fire door finally gave up, I decided to replace it with .120" stainless plate over 1" ceramic blanket.
Just finished and hope it lasts longer than the last one.
I used ceramic blanket under the stainless plate with some heavy gasket material around the edge to help keep the blanket from falling out.
The stainless plate is held in place with 1/4-20 stainless bolts fitted into stainless sleeves to keep the blanket from collapsing.
The pictures are kind of in a backwards order....my fault.