You will have a massive effort to get to where the fangs are with the bumper cover on the car unless you remove the fender wells...and then you might distort the bumper cover when marking and drilling, causing an error.
As you can see, I use three bolts (and large fender washers) in each fang area, not including the fasteners in the center.
The BEST way it to remove the bumper cover from the car. That way you can position it just where you want it before you start to drill.
See Attached.
