To secure the bottom of the fender, I used an aluminum bar to create arms to reach across the wheel. Bend the bar 90 deg. twice so it will fit the inside of the fender. (When it's attached it will actually be less than 90 degrees because the arms spread out a bit)
Cut the arms down to an equal and appropriate length with a hacksaw. It will depend on where they attach to the fork. I'll get to that in the next step.
Rivet the arm to the fender. First drill holes through both and use a pop rivet gun to put 1/8" rivets through. If you cant get a rivet gun maybe you could use short machine screws and nuts.
As you can see in the pictures, originally I was going to connect the aluminum bar to the underside. But then I realized it would be better to rivet it to the walls of the fender so that the arms can rotate where you need them without changing the shape of the fender. So I drilled out the old rivets and put new ones in the sides.