I've used one π's in my cars for a long time. On one occasion, I bolted the cabinets to the passenger compartment firewall that separated the trunk from the back seat. In this installation, the whole speaker system faced forward and was permanently attached. But it is rare that you'll have this as an option and usually only in two seat cars.Cars with a diagonal hatch are another excellent vehicle for this kind of installation. Cars like these have a large bed in their rear hatch. Put velcro pads on the rear of the speakers and lay them on their backs. This works well if the rear window is angled so that it forms a reflector directing high frequencies forward.