Thinking of a Mod for an Offset.

I have a New Braunfels offset that I want to keep and use for sentimental reasons even though I'm going to be making a UDS. The main problem is that the metal is a bit thin. It loses a lot of heat through the top of the fire box. I thought of replacing the door with a thicker piece of metal and overlaying the rest of the top half of the fire box with another layer of sheet metal. I would go to the scrap metal dealer to see if they have any steel pipe the same diameter as the fire box for making a new lid. Messing with the cook chamber wouldn't be worth it. It has been modified since this pic was taken.