You could just get one of these.... http://www.siliconacoustics.com/novibes3.html
You shouldn't need either foam or springs - just solidly mount the case and drive so they don't bounce around and as long as your car suspension is not rock hard then it will be fine.
In my initial install I used little rubber grommets on the screws (screwed into the mounting holes on the bottom of the drive) and kept the screws reasonably loose so the rubber was holding the drive up. Worked fine.
Though in my new case, the drive sits in its own little removable caddy with no shock protection. No issues.
89 Celica, CarPC installed, 1st bday :)
- Epia V8000
- 80GB WD 7200RPM HD
- Xenarc 700TS
- SB Live
- Opus 90W
- CIMR100 remote
- Deluo serial GPS
- D-Link USB radio wired to power antenna
yeah its no problem really most drives can take shocks of a g or two already. Mount it securely and don't worry about it. If your loosely mounted then your more apt to a serious shock.
My car has a hard *** ride, I'm mounting the hard drive on some foam, then I'm using an IDE cable that has the extra bar on top of the connector. I'm going to have the cables go to the drive with a nice gentile s curve in the cables so movement wont fatigue the wires. Just enough foam to take the edge off the vibration and bumps.