I have seen 1 truck done with the durabak, very similar to the Herculiner bedliner, it looked nice at first but started breaking down and the rubber particles started to disintegrate within 8 months.
I agree, it is just not UV stable enough for the job. A higher qualitiy
commercial grade truck bed liner like SpeedLiner has much better
UV stability. (I am a former SpeedLiner installer/dealer)
Also, darker colors have better UV resistance due to higher levels
of pigments.