I just recently installed Koni FSD shocks on only the rear of our motorhome. These shocks function as soft shocks on sharp-edged bumps, and function as stiff shocks for sway control on curves, for controlling air push from passing vehicles, and for controlling the bounce from rough road surfaces, going over curbs, etc..
So far they are performing exactly as advertised and as I had hoped. I intentionally took a trip down a CA highway yesterday with a particularyl torn-up right hand truck lane. The FSD shocks definitley rounded-off the jolting from the cracks and potholes, but continued to maintain sway control just a bit superior to the Ford OEM shocks when they were new. The cracks and potholes on that particular section of highway now feel in the motorhome almost like they do in our family sedan on that same stretch of road.
The Koni FSD shocks carry a liftetime warranty and are expensive. However, you may not feel highway cracks and potholes much in you van with the heavy BMW in the rear. You may need only bounce control when carrying your BMW, and many less expensive types of shocks will control suspension bounce introduced when carrying heavier than stock weight.