In any motorhome the body (sidewalls and roof) just sits on the vehicle chassis and is basically bolted to it. Monaco always claimed they used a "semi-monocoque" design, but in my opinion that was mostly marketing hype. "Semi-monocoque" is much like "partially pregnant". If you are thinking in terms of a steel cage capable of withstanding a rollover, forget it. Whether it is a 1994 or 2014 model.
The main safety advantage in a diesel class A is that you are in a tall and chassis and a heavy vehicle. The driver & passenger are seated well above most things you might run into and the vehicle frame underneath absorbs most of the impact. Plus, a heavy vehicle can absorb a lot more momentum than a light one. It's like a 300 lb guy kicking a 1 lb football. He hardly notices the the impact, but the football flies 60 yards because of the energy imparted to it. In any collision, the big guy always comes out better.