If you are in the USA, head on over to Smartmadness
You can, of course, buy it directly from S-Mann or from S2smarts.
The only prep work required is having the spoiler sprayed to match your car.
In the pack you get a pack of fixing screws, you can use these but I have
always preferred rivets so I decided to use those instead.
Place the lower carrier onto the original spoiler, ensure it is centred
and mark the holes with a pencil.
pilot hole for the supplied screws. Fit your fixings in place to hold the carrier to the original spoiler.
If you use rivets, use suitable washers on the back to stop the rivet pulling through
and damaging the plastic.
None of these fixings will be visible when the top section of the spoiler if fitted.
the curve where the new and old spoiler meet. Remove the top piece again.
This will make it easier to remove excess adhesive.
Using the fine sandpaper, rough up the area where the new and old spoiler will touch.
Wipe down the arear you just sanded with a wet cloth, this will help the adhesive stick.
As you can see from the pictures above, I did the bonding in doors.
No matter how careful you are, you will get bonding agent on the carpet (as I did).
It doesn't come out and anything strong enough to lift it will destroy the carpet.
Always put down a sacrificial towel, large piece of card or something that doesn't belong to you.