What a great thread. The car dealers thought i was nuts for bringing my own plywood test piece.
For the record- 4x8 fits in my 2013 Kia Sorento with 2 feet sticking out the back and tailgate roped shut. it won't lie flat- it must be in the middle widest part of the hatch about 10" above the floor, but it makes the 10 mile trip from the big orange in one piece.