Herc has got quite a roughness to it. And to be effective, it needs to have 2 coats so even as thin as you could make it, it would be fairly thick.
I wouldn't powder coat anything like a bumper as when you scratch it (and you will) it is nearly impossible to match without re-powder coating it.
I recommend finishing the bumper, mocking it up and then roughing it up with a 3M pad, cleaning it with some acetone, 2 coats of self etching primer and the paint of your choice. You'll always have or be able to get matching paint for touch up.