Have you drilled hole in trunk under the spoiler? If not then I strongly recommend to do that. It is needed to avoid deformation of spoiler when temperature changes. Now you can will have to remove interior trim from trunk lid and then make ~3-6mm hole (it is enough with one hole) in trunk somewhere so there is ventilation and pressure can change on temperature change!
Here I made some instructions:
http://www.933motorsport.lv/race/install/ (Sorry if I haven't sent you this info)
Threaded Mode