OP, glad your son fared so well. I've seen many many wrecks due to my profession, and the injuries from said wrecks. Definitely look out for neck injuries, if he has any complaints of head/neck/back pain. Get him looked at immediately.
Again, I'm very happy to hear he is able to walk away from that wreck. about 2 mo ago my step son was airlifted to a hospital 100 miles away...after a rollover in BFE. He too was extremely lucky, no serious injuries. Times like that make you realize just how fragile we all are.
usklx, "a frame under it" is referring to "body on frame construction" of trucks and older cars. New cars are "unibody" where the cars body has the structural rigidity to act as a frame (less weight, which means the EPA is happy b/c improved fuel economy). These cars have"subframes" front and rear that house the suspension and drivetrain bits and bolt to the body. This is both a weakness and a strength, depending on your goals.