its not just a cut and trim the edge job as the panel is hollow, it is 2 ally sheets with strengtheners every so often, if you cut in the position as in the pic geoff shows you need to put in a box section in each half to give strength to the edges and give you something to fix the trim panels to.
top tip time.
dont use a jig saw to cut the panel in half as it is double skin thin ally and your blade will wander all over either top or bottom skin and maybe make them different, use an angle grinder or similar this cuts straight and doesnt grab the fabric it melts it as it cuts.
