Spoilers delivered, with the tailgate

Spoiler was delivered today, attached to the tailgate. I was planning to just swap it over leaving the spoiler on the original tailgate door, but the connections and pipe have all been cut so this might be a non starter. I can see the Cup Spoiler is held on with 4 bolts, how difficult is it to drill the holes? Something about taking a drill to metal paintwork seriously stresses me out.

Anyone got experience fitting spoilers?
Thanks
 
Does anyone know what this backing foam pad thing is called, seems like very thin soft padding, can't find anything online to replace it as it's all perished, assume it needs to be waterproof as well.
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I think it's just there to protect the paint get some of the double sided foam tape should be ok..