No, an HDD should not be left unsecured inside a case.
No, an HDD should not be left unsecured inside a case.
The situation doesn't require any 3.5 inch bays. You can secure it by screwing it directly onto the base of the case. Since you don’t have mounting hardware, it won’t be attached but rather placed on the bottom.
I’d consider securing it more firmly by adding extra tape or reinforcing the area. You could also use screws and mounting trays if you needed a more permanent setup.
I’m unsure about the exact setup of this scenario, so I can’t say for sure if it includes vibration dampening. It might be worth reaching out to the manufacturer—they designed the case and likely have the necessary components.