This is much easier than making a plug, then a mould, then making a part from the mould, just make some sheet on a plastic tile, slightly deliberately curved in this case and cut off what you want and stitch the edges together with either soft metal garden/child's toy ties or, as I did, araldite and temporary fat washers on each side of adjacent panels.I learned this technique from a posting by Royce Creasey as he built a new CX500Banana fairing for Bob Winsper.Recommended by Andrew Gibbens who designed the ComfortMax topbox (which I use) is that you resin on wide 40mm bandages either side of the join to reinforce the edges so they do not split under strain, when I prop open the topbox lid in my case and fill it with jacket, helmet, food and drink :)