I have had a " work in progress " for about two years now. I had all my thoughts together and when I went to cutting.......well.....One thing or another has kept me from finishing it.
I can tell you from experience that the metal is going to flex when you cut it. If the section that I had cut out would have maintained it's shape then I would be done already.
At 48" overall length, I would recomend building it UDS style....You can't go wrong with that design. It might be a little long after you mount some feet on it. I would cut the top off and make a lid. I would cut the section directly under the lid to give you an overall height of around 40" from the bottom of the feet to the top edge of the cooking section below the lid.
What I am describing you is exactly what I plan to do to my other " work in progress" that I have only had for one year.