It's much like unibody car repair: You used to be able to bolt a hitch, bumper, roll cage, or winch to the ladder frame of your vehicle. The ladder frame was ba

It's much like unibody car repair: You used to be able to bolt a hitch, bumper, roll cage, or winch to the ladder frame of your vehicle. The ladder frame was basically a pair of ~2x5" C-channel heavy steel bars running the length of the vehicle, with crossmembers linking them together. It's still present on a lot of trucks, and some SUVs, but more and more vehicles are moving towards lighter unibody construction. In particular, this helps with impact safety, because the unibody can form crumple zones. A ladder frame doesn't crumple. Now, most vehicles don't have ladder frames. If you want to drill a hole for attaching a bolt, for example to add a tow hook, you probably need to first weld on a 1/4" plate. A body shop can't just un-bolt a rocker panel damaged in an accident and put on new ones, both rocker panels are one big piece that forms part of the structure of the vehicle and everything else is connected to them. You cut and weld to repair the damage, or bend it back into place. In race vehicles and motorcycles, this concept is extended to the engine itself: The block is a structural member of the vehicle. Practice will adjust to progress. It won't always be as easy to repair as it once was. We can only hope that the safety and energy improvements are worth the complexity and functionality.