A common issue in rallying.... hitting trees sideways. A way to set up the seats better is to run 2 smaller tubes sideways across the floor for the seat to bolt to. Weld the outer ends to a sill tube preferably, or the rocker if no sill bar is installed; put the other ends through slightly larger 'slip' tubes welded to/through the tunnel. In that way, the the seat can move inward a bit if you have a hard sideways hit that crushes in the side bar, sill bar, and rocker on the driver's side.
Sounds like the victim suffered a basilar skull fracture.... same thing that got Dale Earnhart. The only way to have a hope to survive this is a head & neck restraint like a HANS or Simpson Hybrid or similar device that is SFI 38.1. They are not really rated for 100% sideways impacts; the only thing for full side impacts is side nets and on both sides of you head, or a seat with wings by your head.
We have to have the H&N restraints for all sanctioned rallying now... no exceptions. The side head support is not mandated.
