Cut a short length of inner tube a bit longer than what you need, trim it straight up the middle.
Try it for size and draw where you need to cut.
Hold the tabs around the back of the forks and zip tie together.Finished article looks ok and works, cheaper than a shop bought one and greener too. This is one I have used but there are many ways it can be done, I always use a CRUD CATCHER front mudguard aswell as downtube and rear mudguard. Period!