Ok maybe a little worry here. Having a lot of equipment in the truck, dropping a lot of it in the sleeper, I have yet has a hard drive fail on me, even with a few that have been running for 5 years in servers.
If one is to worry about the shock of the truck and so on, then maybe instead of going to all the problem of building a shock proof cage, just do what I did for a former customer. He had a carputer that was installed in a very hard riding 4X4 because he was so worried about shock, he would barely use it. I took a 160gb 2.5 laptop drive, got one of them external USB drive case and cut some used accostical tile (the foamy stuff) for the base of the drive case. Glued it on the bottom of the case, and then placed it inside a destop computer case with two tie wraps to keep it from laterally moving (fits perfectly). It was a simple solution for his worry, I think he has had now some 7000 hours on the box, and some of that is very harsh driving. The 2.5 drive is made for higher temps, and now with the 500gb version, it makes sense to use them.