When you are doing a synthetic stock with hard rubberized grip panels, can you coat them or should I mask them off?   Also do I need to stay at a lower temp to keep them from delaminating?  Say 150 instead of the recommended 180.  I can call NIC but wanted to get your experiences if possible.  Thanks.  

This is what makes me think it might hold up if you could get it to adhere (obviously).  

I have done them before and they seemed to work just fine.
However, 5 years down the road who knows? If it were to wear, it would probably wear there first.

The single direction flex like the ASTM test isn't the problem on soft substrates. It the back and forth of the flexing that will eventually fatigue the Cerakote, just like bending a coat hanger over and over.

Keep the temp at 150 and you should be fine.