[franken]

There are no exterior panels that used 18 gauge metal from the factory, and certainly none of the aftermarket ones.

The aftermarket panels use some metric gauge close to the 21 or so gauge used by GM. You can look at 18, 21, Asian patch panel, and a cut out of factory metal. 18 gauge is almost twice as thick. You can measure to prove this for yourself as well as look up gauge vs. thickness of steel. Note that a sheared edge will seem thicker since it gets rolled a bit when sheared. You need to cut a scrap out and measure.

I've seen Triplus stickers on Goodmark and Dynacorn parts and agree that there are few places actually making the parts, but many distributors selling them, as well as quite a few middlemen.

It also seems that quality is sort of the luck of the draw. You may get a great part, while mine is junk...