Here are a couple of preliminary pix of the bottom fender mount. The skateboard bushing has been cut a little bit to match the curvature of the fender. I didn't take time to center the bushing too well, so don't worry about the misalignment you see in the picture. You could also use a cupped steel washer between the bung and the bushing, like on a skateboard. I have both a chromed washer and a black one. It is drilled and tapped for 5/16-18 NC threads, and I have an Allen head screw run though the fender.
Please let me know what you think... I have another question on the top mounts, but I need to create a picture to explain what I am asking.