All of the diorama's I've done have been rusted relics. I like the idea of a vehicle that has been used, is past its prime, and has been forgotten by most. The viewer can use his imagination as to where its been, how it was used, and how it ended up where it is. No one comes up with the same story, which is in my opinion part of the charm behind this kind of display.
Mine all have a "front " side, but can just as easily be viewed from all sides.