What's the best method of drilling holes on back deck?

[Rotech]

Hi, I am planning to install 6x9 speakers on rear deck and I was wondering the best method of drilling holes since I can't drill verticall on a Malibu.

 

[454GrandPrix]

Instead of drilling holes, you could just get some of these 4x10-to-6x9 speaker adapters.

https://www.amazon.com/dp/B00009QOP4/?tag=gbody-20

That's what I did, anyway.

 

[565bbchevy]

I used a 90 degree cut off wheel to notch the deck and open up the holes for flush mount 6 x 9"s