I don't really have anything to offer, just that this has been a concern for me for several years. I kept my daughter in her full harness seat for as long as possible. Now, I just make sure we stay off the highway, and out of busy traffic. Sometimes I wish I had a hardtop instead of a convertible.

Again, not any help, but I'm planning on a custom cage for the rear of my K5 with shoulder belts for the kids. Unless I trade for the FJ40, then the K5 will either be my toy, or get sold, and the FJ already has a roll bar that I can hopefully add shoulder belts to.