Agree with the above as to "50+ year old trunk mat". On the Chryslers, the lower-level models (as Newports) had a thick, molded-pattern rubber mat. Rubber got old and brittle. Moving them disintegrated them, by observation. Replace with carpet from New Yorkers, with the correct side "bindings", non-rubber-coated backing, to protect the floorpan from condensate accumulation on the back of the rubber mat. Perhaps the thinner vinyl mats are not quite so succeptible to such condensate accumulation?
My '70 Dodge Monaco Brougham had the carpet trunk mat from the factory. NO evidence of condensate ever accumulating in the stiffening beads on the trunk floor. Go black in color with a matching spare tire cover. Might not be "factory", but will look nice and protect the trunk floor in the future. FWIW, the pattern on the '66 and '67 Chrysler Newport trunk mats mimicked the loop carpeting inside the car.
Just some thoughts,
CBODY67