Moar update
I was done leveling up like crazy in Borderlands so I tried to give some thought to mounting the HDD.
I decided to stick it below where the PS3's card reader would normally be.
I laid the drive where it was supposed to be, marked the holes with Sharpie, scratched out rudimentary 'pilot crosses' so the bit wouldn't wander and drilled them out. Then I tapped them to M3 for some extra grip from the bolts.
This is what I ended up with:
It's held in place by only two M3 button heads, and it
seems fine. What I'm worried about is whether hanging off two screws, even if it seems stable now, might bugger up the drive in the long run. I might glue in a hanging a plexi support on the inside if I can squeeze in the extra space but it's because the build is cramped that I have to compromise in the first place.
EDIT: First post now has a list of updates in chronological order.