If it's black it's ABS if it's white it's PVC. The one's I've seen have been ABS.
'11 GMC 3500hd SLT DRW D/A 4x4 Spray-in, Air Bags w/comp & controls, TL, Superhitch, 48" Supertruss, 9.5t Warn, front rcvr, Fox Shocks, '11 AF 1140, DB, AC, Gen, Solar, Thermal Windows, Wardrobe, Rear & Side Awnings, 18' Lund/40hp Honda 4 stroke