I work in a car bodyshop we undertake accident damage, chassis damage, full resprays etc.. I had never stuck a spoiler on anything before other than a fiesta zetec s that already had the holes to mount one. So what I did in the end was used double sided tape all around the edges and then covered the whole outer areas in a product called "sikaflex" which is actually a marine sealant, it holds even at 120 mph lol so must be fit for the job. If anybody else attempts to glue a spoiler on I can not recommend it enough.