Yes. 100% for-sure! If you are wondering whether your Chevy Uplander-based minivan will hold full sheets of flat stock, here is your proof. Fresh from the Mega-lo-Mart, here is our 2005 with THREE full sheets of plywood in the back.
Keep the drive home short, though, because the driving position is . . . uncomfortable and unsafe. The rear chairs do not need to be removed, they can be folded (they are folded in these pictures). The front chairs need to be all the way forward and all the way upright, and the back hatch will close when the plywood is pushing against your chair. The sides will scratch on the trim by the back seats, and the seatbelts will get splinters or at least be rubbed pretty hard. The power outlet (if your car has one) may take a beating if you are not careful.
This is all the room you get. But it fits. . . . barely