No paint on bed liner will prevents dents.
Full Metal Jacket is applied at 800 degrees and is put on thick, but still can't prevent dents. I know. I threw a 2X4 in the back of a friends truck and it dented the wheel well. He wasn't pleased.

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"Tell it like it is or don't tell it at all" 1964 Falcon 2dr HT, 347V8 4V, dual exhaust, 5sp, pwr assist R&P steering, AM radio, heater with defrost and 2sp fan, electric windshield wipers, cigar lighter, dlx light group, bucket seats, console and full carpet.