I got the spoiler from Ebay and had it painted by a local garage.
Step one.
place some masking tape on your boot to protect it from scratches while test fitting the spoiler.
Step two.
using the templates provided pop the guides into the holes under the spoiler and stick them to it using a tiny amount of tape, arrange the spoiler on the boot of the car with the templates sticking out of the sides.
when your happy with the location of the spoiler stick the template guides to the boot with lots of tape as seen here.

when you have done both sides you should have something like this.

Step three.
Next up is drilling, the templates and the tape really make this easy.

Step four.
After drilling the pilot holes using the templates remove them but leave the masking tape on the boot until you have drilled the holes big enough for the screws to fit through. I also had to drill a 3rd hole for the power cable for the brake light.
Step five.
I had to drill some access holes in the underside of the boot to allow access to the screws that hold on the spoiler as seen here with the blue arrow. Again I used some tape to stop the drill bit slipping.

Step six.
Once you have all your holes drilled. remove the masking tape and line up your rubber seals. these ones stick to the car so make sure to do pleanty of test fitting to make sure they are in the best place before you stick them on.

when you have them both on, you will have something that looks like this.

Step seven.
Fit the spoiler on the rubber seals and screw it on, making sure to route your wire.
getting the screws into the holes was maybe the most tricky part. I taped the screw to the end of one of the template guides to hold it in place and then screwed it in using the access holes made earlier.
when you have finished it should look something like this.

Step eight.
Now the only thing left to do is to wire up the light, Mine is wired up to one of the brake lights on the back, after fitting all the carpets back in the boot there's no wires to see and in the dark it looks like this