make sure you line everything up, double check it and double check it again, thats stuff is strong you will have some issues getting it off again, and you will look like a silly a*se with a wonky spoiler!
the genuine spoilers have 4 6mm bolts that you take off, and where the washer jet is theres 2 torque screws, when you remove them the spoiler can be prised off as its just held down with 3m double sided tape, then the backing plates helps on with 4 10mm plastic bolts as the corsa tailgates with the factory spoiler have small threaded section welded on,
so thats the genuine one lol
the cheapo replicas are usually the worst fit ever but come with wee sticky tabs that you put into the screw holes on the spoiler, you then get a mate and yourself to line the spoiler up and put preasure on it till the tabs stick to the tailgate, you then drill through the middle of the tabs and this gives you the mounting points needed, then its a case of a wee bit of threaded rod in each of the holds and use the 10mm bolts supplied to draw the spoiler down till your happy with it, but i must warn the replicas are never that hot
tigerseal will be good to a point, but i still wouldnt just bond it on and leave it at that, id hate to be driving along the road and to get hit buy your spoiler a few months down the line, use panel wipe to clean the surface, get it from halfords and all good motorfactors, and do not use a degreaser they leave a covering that will react with the tigerseal
i suggest tigerseal but id try and find a way of a bit of added security as if at some point it comes loose you wouldnt want a claim on your hands cause of somthing as simply as a cheap spoiler, id try and run a selftaper screw the tailgate and into the spoiler on all 4 corners, this will make it 100% secure and also draw the spoiler in making it sit a lot more flush