I used the 3M outdoor tape (red tape). Held on for 2 years so far, no problems.

 

Im trying to put my trunk spoiler on tomorrow and was wondering if I should use the adhesive promoter they gave me. If yes, how do I use it exactly? Do I apply it to the tape or the trunk itself? Thanks.

 

Use the promoter and apply is to the trunk.Makes the surface tacky for a better grip.
Any excess around the spoiler can be cleaned easily with alcohol.

 

I think people need to chime in & say which rear spoiler they have, I got one off Ebay & it never really fit right & even with the 3M tape in never stayed on, So personally If you buy the cheap one off ebay be careful, you may get a gimpy one like mine & no matter what 3M you use in wont properly stay on. I got so frustrated I went out & got the IS-F rear spoiler (which I liked better) & just drilled holes with the 3M tape & lets just say that thing was on & never coming off.

 

got the OEM trunk fin/spoiler which came with double sided tape (not sure if it was 3M). It held for about two year but since people at times hold the spoiler to close the trunk, it eventually came off.
I have some other tape (not sure which kind body shop used) which it's holding up good. Will take it off and redo because I can see the tape all along (looks pretty cheap).
I will personally buy the best tape next time and do it myself.

 

YEAH. Works really well