Fitted the spoiler at the weekend. Initially used the 3M tape supplied with it, but there wasn't enough so had to pull it all off and start over. Glad I did actually, as the Gorilla tape seems a lot stronger.
Used the technique described in the fitting guide provided by
chedixon - thanks buddy
As there was no existing spoiler to get the position, I placed the new spoiler where I wanted it, then used masking tape to mark the edges so I knew where to place it when fitting for real.
Pretty chuffed with the result. Hopefully it'll last....