I recently got a flat tire and changed it out with the donut in the back. I stupidly left the flat in the trunk. Now the trunk, aka the cardboard, is warped. Anyone know how I can replace this or what part number it might be?

 

leave it in the sun with something heavy on top. or just make a new trunk floor out of thin plywood. thats what im going to do next week

 

I would use hardboard over plywood, given the thickness of it, if you're building a replacement.

 

Screw it down to a piece of plywood

 

have you tried flipping it over and attempted to warp it again? (hopefully, back to being flat).