Mike, when you cooked these potatoes on the grill, did you put them directly on the grates, or did you put the iron skillet full of potatoes on the grill?
I haven't seen a post from Dean Torges in about 4 years and he has been missed. His posts were always interesting and informative. Hope he is well.
Dean suggests using a heavyweight cookie sheet. If yours are on the thin side, you might try double-panning two cookie sheets.
Also, to facilitate browning, one could preheat a pizza stone while the oven preheats (for at least 1/2 hour, preferably longer) and put the cookie sheet on top of that.
Randy's suggestion of using the Reynolds nonstick foil sounds like a great idea; it might even work in an iron skillet that might not be too well seasoned.
Rita