Mate, I just drilled my own spoiler, I didn't find it too difficult. Make sure you've got the right drill bit type first (ie metal drill rather than timber boring drill). Secondly, use a small drill bit to make a guide point in the metal (much easier to get the exact right spot using the template then). Thirdly, before drilling each hole coat the paint with an anti-rust spray (use a bit of masking tape to make sure it doesn't drip down onto your window) - this spray will both lubricate your drillbit as it drills and will obviously serve to anti-rust. Finally, spray the holes comprehensively with the anti-rust spray before putting in the screw-locks. I also sprayed the screws, and after I'd finished screwing them in I sprayed on top of them as well.
Truthfully, it's a pretty easy process.
And I'd never trust 3M tape to hold onto my spoiler at 120km/hr. Especially when it's attached to a non-porous gloss paint surface.
