You really need a Counter sink bit- not a Drill Bit.
There isn't much meat there to work with and Drill Bits tend to Grab and drill on through, like they're supposed to do and then you end up with a very big hole.
I would try a Round Head Bolt first and see if you can ride with it that way.
If the Bolt Heads bug you, then buy a Counter sink bit and use Flat Head Bolts.
Since the Deck is Aluminum(soft metal), you can use a Counter Sink bit made for wood, which can be purchased at Lowes/Home Depot/ Ace hardware stores