spoiler

Is hollow and there's no need in there for you to drill or screw into so if you use like a self-drilling self-threading screw do not over tighten it make sure your clutch is set to almost nothing so it zips in and stops because there's no meat in the spoiler at all It is just hollow and you know it's just sitting on these like clips that's how it's held to the car You should look at some pictures if that interest you but yes it is very hollow and like what would you be screwing in to that spoiler like a high lift racer wing it's not going to last a minute You need to go with quarter 20 bolts and washers all the way through the spoiler but the nuts on the bottom and run them up to touch with some loctite The spoiler is so thin when you run the quarter 20 up to the washers it'll start squashing the spoiler almost immediately

 

I'd recommend you take the spoiler off so you know the what where and why of what you want to do with it.
The Gen 4 spoiler is also hollow and is held on to the hatch by 7 plastic clips that are in 2 opposing rows.
The opposing row of clips make it more difficult to remove without breaking at least one or two of the clip mounts on the spoiler, but they can be glued back in place if not mangled too bad.
A trim tool set of a large and small tool is all that's really needed to pull the spoiler, other tools can be helpful too. This is the best time of year to do it. as the clips snap real easy when they're cold.
With the spoiler off you'll see if you really want to mount something else on it and have access to get it in just the right spot.