Haven't given a whole lot of thought to the repair but the rust cancer is quite extensive. There just isn't much metal left. I'm "thinking" cut out all that is not stable, screw a 1/4" plywood from the bottom to create a floor, lay plastic sheeting on top hardware cloth, use 1/2" hardware cloth to form the floor and side walls, lay chopped strand fiberglass with resin. Followed by matting on bottom underside. Better than $1000 - $1300 the body shop wants! (Ridiculous amount for maybe about 3-4 hours work!)