[MultipleParadox]

Localized heating will have WAY much more chance to warp anything than heating uniformly the whole piece. The high temp you will have at one spot will dilate much more than the lower temp spots, let alone the parts still cold which will not dilate at all. Result, warping.

Oven would be the way to go. If you've got a convection oven, even better. I would say use that.

Disclaimer:
I'm in no way knowledgeable about dura/arma-coat, or never had to bake any metal piece like that. But to me, this is just common sense. Take it for what it is