Wouldnt you need a shock proof hard drive?
not really you could use an ssd but yes there very expensive and very slow at reading & writing large portions of data, a standard hdd will do fine if it is moved very suddenly then the head will scratch the traces on the drive so if you hit a speedbump doing 30 it would probably damage it
use a laptop hard drive (they're built to survive knocks a little better) and suspend it in a frame from springs.
so it is free to move around but it wont get jolted. i've seen somewhere on the net, a guy used rubberbands but they will age eventually and could fail.
some relatively weak springs would do the job much better, i'll have a quick hunt but cant promise any pics.