You can do this....if 3D does not provide a template (call and ask them), then you will have to make your own; that would be the hardest part, which it is not hard to do; just use the spoiler itself to make a cardboard template from, using the edge of the spoiler and trunk lid as your guide.
Once you have marked the points for drilling the holes, place some masking tape over the spot and mark for the holes again. The masking tape serves two purposes: one, it helps keep the drill bit from "wandering" when you first start, and two, it keeps the paint from chipping. Start with a small drill bit, then work up with a second size, then the final drill bit size. Remove the tape, then take any color paint and dab it around the edge of the holes you just drilled; the spoiler covers up the hole, so any color works for this.
Theres a debate as to if two sided tape is required; I did not use any, as removing my stock spoiler took an act of god and a good hour to do, as that 3M automotive tape was tough! Some say to use it to help keep water from getting underneath the spoiler. I did not use any when I installed my 3D GT500 rear deck spoiler, and I do not have any issues with trapped water.
It is better to keep your mouth closed and let people think you are a fool than to open it and remove all doubt.