For the entirety of college (dont ask me how long, lets just say more than 4 years) I moved twice a year to college and back home. Now, I lived in Alaska. So each move was a 16 hour drive with some pretty bumpy sections. Some of the worst parts were in Canada funnily enough...
Wanna know my secret? Just jam the case somewhere so it doesnt move. For me, that was put it on the floor in the backseat and slide the front passenger seat back until it squeezes the case. Now it doesnt move more than the car moves.
Now, cars dont actually move that much, you feel it because your head isnt clamped to the car, its on your neck and is flexible.
Unless your going through speedbumps at top speed every 30 seconds, your PC will be fine as long as you "attach" it to your car. Carmakers have spent millions of dollars on suspension systems so cars have largely just stopped shaking apart constantly, use that R&D.
I have never had a hard drive fail due to those trips, and many of them have been through at least 6 trips ~16x6x2=190+ hrs of driving with that simple solution. Didnt bother laying anything down for the video card/cpu cooler bouncing. And I did use aircooling back then.
Now, some of the coolers are bigger, and the GPU's are definitely bigger, but as an engineer (passed license exam, just waiting on bureaucracy) I can tell you its the jerk (acceleration of acceleration) that kills things, not the "gentle" bouncing you'd get with a normal car ride.