How about the walls are also on a LPS chassis? The walls move around as well as the vehicles. The projectors, too. In fact, let's put the black box on wheels and you can have one line that goes up to a black box and when it's filled, it moves out of the way for the next black box.
Or, make the black box small. Small enough for one vehicle. Maybe a semi-sphere around the vehicle for the projection and you sit in a pod with a handful other people. And the pod moves around in sync with the projections. And just like my idea above for the black boxes to be on wheels, this small black boxes would also move to accommodate the next group. Well, maybe not wheels, but how about a big turntable?
Then you can just update the pod and projections. The perfect black box.