They also effectively keep dust, dirt and moisture from entering the engine compartment around the lighting area.

A better method is to actually take your headlights out (not difficult to do - a couple of bolts) and apply trim adhesive (It comes in black - buy from Pep Boys). If you take out the lights, you'll get a better bond and can get them to look "factory." I did not remove my lights and there are gaps around the lens/trim that could look way better.

-- John