@rpardee
That case design is a horror show. Standard practice for Dell, though.
I don't see any good place to mount a 3.5 in HDD.
If I were you, I would park that drive right on top of the power supply, with these under the 4 corners to reduce vibration and to keep it from scooting around.
https://www.amazon.com/Moongel-RTOM-Resonance-Pads/dp/B00GXNZP80/
@rpardee
Also, putting heavy things on top of a laptop is risking some very expensive damage.
@voltronic Ah--thanks for the advice! I suppose it may come to that. :( I wonder if I wouldn't be better off just buying a housing for this thing & running it as an external drive... Tho then I guess I have to power that separately (right?). Probably a PITA.
Amazingly, the new machine is pretty light, tho I totally take your point...
@rpardee
If there is an eSATA port on this motherboard, then maybe. I doubt it has one. USB will be much slower so I don't recommend it unless it's USB-C or if you need this to be a portable drive.
@FreedomATX
Uh, I hope you're kidding.
Depending on where the glue goes on the enclosure, I'd give it as high as 50/50 that the glue stays solid during use!
@voltronic @rpardee
Hot glue it to the PSU enclosure.