I have started working on my prototype part which will cover the section of tire which the stock bumper does not. This was supposed to be a final piece but I wasn't cutting straight so it doesn't fit how ever I will be making more cardboard models until I get the edge contour perfect.
Once I have the desired exact dimensions, I will cut the plastic almost identical to what you see here, give the inner edge a 45° angle so it can flush mount to the bumper, and attach it in the back with 2 mounting locations, at least. The leading edge will be sealed with a rubber gasket I have left over from truck flares, or some RTV if I can't find the gasket.