I 1st got the ****ty one sold by MAS. Complete junk, there is no bottom to it and it is not a bolt on deal. Actually there is no way to bolt it on, and dosen't clear the body line.
Then I got the real one from 1st place. Their spoiler is awsome. Fit was perfect, they make it so it clears the body line going down the middle. Expensive, but it is worth it. Its plastic, not fiberglass, and required only final blocking before paint.
The drawing above was not 100% correct for mine (but it is very close), I just lined it up and marked it from the spoiler directly. There wasn't any cutouts in the backside of the deck lid on mine, for the brackets. I ended up drilling 1/8" dia. thru from the top, then on the underside, used a special cutter that the body shop had. It was like a 1/2" hole saw cutter, but used a 1/8" guide pin to follow the pre-drilled hole. That gave a nice cut thru the backside channeling. Then oval'ed out that 1/2" hole with a tree shaped burr. It will need to be a good sized hole so the nut and a socket will fit thru to tighten it.