Mike ,
I don't think the can will get hot enough to destroy powder coat , as long as you don't sit still for long periods with the motor running , which is a bad anyway . The can being in front and air flow drawing heat away should keep it 'cool' enough .
I used regular flat black paint on my muffler and it hasn't been effected at all . BUT , my muffler has a deflector inside which directs the exhaust to the sides , then down and out the tail pipes . So , the exhaust doesn't hit the outside of the 'can' directly .
Pete .
