Ok I think I figured out my back door.
The snow has been melting, and beside my garage I found some metal that I salvaged last year.
I forgot it was there.
Nice heavy steel, 2 pieces.
1 x 1 square tube.
3 ft wide 7 1/2 ft tall
So after I cut it down, I can cross brace the middle.
I will leave the one at 36 inches wide and just cut the width of the second one.
Hinges on the sides attached to the existing door frame.
Skin the outside with aluminum and rivets.
Inside, i can put a layer of pink styrofoam insulation, a layer of 3/8 plywood, and skin it with aluminum.
I don’t see a problem here.
Just gotta figure out a couple of the details.