[AzNightmare]

I've been doing a lot of research, but I'm getting different info,
either because of different opinions or different circumstances (hatch/sedan), and it's starting to confuse me.

When I'm attaching the spoiler, I drill holes in my trunk/hatch door, and bolt it.
Now do I need a rubber gasket to prevent water from getting in?
There MIGHT be a double sided 3M foam gasket, which I'm not sure if it's supposed to do the same thing?
I have also read to use silicon around the bolts.

I'm not sure what's exactly required nor what any of this is for?
Is the gasket to prevent water from seeping in? or prevent vibration?? etc.