i have the plastiboard cut/fitted to the trunk floor & the regular trunk mat on top of that. if u use cardboard & it gets wet, it will stick to the normal spatter paint that we use.
I like to use that gray felt over factory cardboard and the steel sheetmetal with spray adhesive. It forms to the contours very well, and looks great when done. I use an extra piece cut to the shape of the trunk floor on top to protect it from whatever I put in there. (folding chairs etc.) When the mat gets dirty, I just shake it off and it's like new again. It's not as original, but it all matches and looks really nice. :TU:
