measure twice drill once champ.. you dont want a bootlid that looks like a sieve.
meausre the width of the bootlid, get the centre point, measure how far apart the bolts on the spoiler are, take half of that measuerment, and measure that on the bootlid from the centre point. this way, the spoiler is centred.
make sure its straight too.. you dont want a funky new spoiler that is mounted crooked.