But you can drill through the thicker pieces. Start with a small metal bit and work your way up in size. I would think drilling into the thicker sections to be ideal?
Same here, why would you want to drill into the thin parts for the attachment points? They can't be using anything too crazy for the reinforcement material that some high speed steel bits cant eat through. Like poster above said take your time with a small drill bit, then work your way up in size until close to the diameter of the screw. Not sure what type of screws the kit came with but you may want to replace with some self-tapping sheet metal screws since going into metal if that's not what they provide already.