Sound's like to do it the first time bumper off is the way to go... But once the speedbumps / multistoreys have had their wicked way and you need to replace, the holes are already there...
 
Sound's like to do it the first time bumper off is the way to go... But once the speedbumps / multistoreys have had their wicked way and you need to replace, the holes are already there...

Precisely, pull old splitter off and use it as a template over the new splitter to drill the holes. Simple case of getting the nose up in the air reaching under and fixing it to the bumper then.
 
Ive had mine in the garage for about 6months! bought it because I scuffed the bumper and planned to get it sorted out before sticking it on.
IMO it looks like some people leave it sticking out at the front a bit too much, i want mine a bit more discreet