Secondly, it keeps mud splatter from covering the back windshield. Since I ride on the dirt/gravel trail, this is actually pretty important too.
As you can see from the picture, I drilled a hole in the frame to mount the fender. The hardware that came with the fender works for this installation and the only modification was to bend the tie bars near the mounting bracket. This isn't a perfect installation since there isn't much clearance above the back wheel and the bottom of the storage tray. I also tried to use the bracket provided with the fender by drilling a hole in the ELF just below the OT logo. You can see the screw there that would hold that bracket. Unfortunately, the clearance above the wheel wasn't high enough, so the bracket rubbed on the wheel. Without the bracket, the fender occasionally rubs on the wheel and needs to be re-centered by hand. But it's not been much of a problem and I've been removing the fender (only 2 screws) when the forecast is clear.
The front of the fender is just sitting on top of the parking brake. This keeps it from rubbing on the front of the wheel. I've thought about using a twist tie to hold it in place but so far it hasn't been necessary since it seems to be staying and it's easier to remove the fender without it.
Although the hardware that comes with the fender work pretty well, I recommend replacing the screws and nuts with ones that fit the installation better.