My walls are all held together with rivets - I took off one side and insulated (though the insulation in there was in very good shape). I did add roofing weather shield against the outside wall.
I did not put sheet metal back - I used wood. And I added my electrical through conduit after the wall - so that I could easily access it in the future. I ran the conduit just above the seat rail.
There is no one way to do it - so gather as much information as you can and do what works best for you.