The saga continues. This is retarded. I got a titanium bit, made the holes just fine, only to find out that the door is essentially HOLLOW.
?!?!?!
I know nothing about doors but didn't expect it to be empty inside. So it looks like it's basically sheet metal on both sides (maybe like 3-4mm thick) with some light 'stuffing' inside.
So, I can't use wood screws as there's nothing to screw. Do I need to get sheet metal screws then? Not sure how I'm going to secure it otherwise.
3 or 4mm isn't a lot. I don't think self-tapping screws are going to work. They will initially but over time I don't think there is enough metal to keep them in place,
Since you can't reach inside the door and use bolts, nuts and washers to secure it, you might want to consider rivets. The riveting tool will compress the soft metal of the collar so that you get secure points of attachment.
However you need to choose the length of the rivet to match the material you're attaching them to. Too short and you'll either pull the collar through or distort it so much it won't work. Then you might have to try to drill out your mistake.
Too long and you won't get a tight fit. So double check the thickness of the metal. Since it sounds like it's thicker than sheet metal, you probably don't want to go with the shortest rivets but ask someone ask the hardware store who knows what they're doing.