Aaaw man - you guys beat me to it... Some additional ideas!
1. Instead of cutting the fender metal
Get a ruler and drill holes. Then mask and spray with matte black.
Black paint helps disguise the cutting, holes do the venting.
2. Instead of cutting all the way through the garnish
Drill holes through the garnish. This will keep the arm (where the chrome mounts) decently strong. Paint the "valley" black to help disguise the holes. Take the old black garnish trim and cut the vent material to match it. What you see through the vent material is black.
You keep the structural integrity of the garnish and keep the look.