Personally I think you need more then some L brackets on the bottom.
Where that stake pocket was is nothing but a large area of flat sheetmetal. Flat metal has NO strength, its floppy.
Even with the tailgate up I see it flopping over all over because it has no strength to hold itself together.
If you ever get behind a pickup with the tailgate down or missing, you will see the bedsides move side to side, in and out. Thats a modern day truck with inner and outer bedsides.
You are talking basically nothing more then a flat piece of metal with some L brackets on the bottom.
