Thank goodness the local lumberyard/boxstore provides up to three free cuts of sheet plywood. With one transverse cut (31.5″) and one longitudinal (23.5″) I was able to A) avoid having to make some very long cuts with a circular saw and more importantly B) fit the full sheet inside the Smart ForTwo.
Well, being more honest, that back window is not quite closed. There is a good .75″ too much length to latch it. But it drove just fine. Wait until I have to bring home two 2×4 studs… that rear window will be almost wide open, and dragging a lot of exhaust into the beasty.