These were removed from my G Wagen around 10 years ago. I have three of these arches, one rear and both front. They are made of a rubberised material, likely OEM.
NEW ODDMENT TRAY Storage Box for Mercedes Benz G wagon G CLASS W463 G500 G55 G63
Pair Headlight Surround with Smoked DRL Mercedes-Benz G-Class G Wagon W463
MANN CUK2545 Cabin Air Filter For Mercedes-Benz G-Class G 500 (463.240, 463.241)
Mercedes Benz G Wagon Spare Wheel Cover fit 16inch wheel only OEM
Interior Blower Motor For Mercedes-Benz G-Class W463 G270-G63 G65 AMG