"Dashcam & rear cam in the next rig for sure! In this case neither would have helped as the rig was parked & unattended so no cams would have been recording."
I don't know the how-much, or how-it-works on these cams, okay?
I used to drive for a subcontractor to the U.S. railroads, transporting rail crews. Our vans had cameras in them (aiming forward and inward). If I understand correctly, they were running continuously (even when parked), but only started RECORDING with impact or centrifical force. Then they would record 8 seconds before the impact, and (I think) 4 seconds after impact.
The dashcam recordings that you see on YouTube are not the only types available, but you need to talk to someone who really knows the business, not some kid at WalMart.