<<legend:
green - veritcally stored 4x8 between front seats
red - 4x8 stored over head
purple - 4x10 aluminum curled downward, stored over head
blue - tilted 4x8 (terrible option)
>>
You and I think alike. I ruled out the TC because a 4x8 sheet wouldn't fit inside, but I kept thinking about it and considered some of these same options that you did. I went to a dealer and took measurements and this is what I concluded.
green: might fit, but it would sit on the center console, which might get damaged. It would also block the driver from seeing anything on the right side of the vehicle.
red and blue: the vehicle is something like 43 in. wide at the level above the seats, so not wide enough for that arrangement.
I also considered hauling a 4x8 sheet on edge, diagonally across the bed, with one end in the driver side rear corner and the other end behind the passenger seat. I measured that distance with the passenger seat moved all the way forward. It didn't look like it would quite fit but someone on this forum said he's hauled like that before.
I did like you and kept thinking about it. I finally decided that my best bet would be the roof rack. So I went ahead and ordered a TC. I'm still waiting on it.