It almost killed me to buy and use corn syrup, but I thought the recipe would suffer without it. Taste of Home recommends this substitute for corn syrup:
For each cup of light corn syrup in a recipe, substitute 1 cup of sugar and 1/4 cup water. For each cup of dark corn syrup, substitute 1 cup of packed brown sugar and 1/4 cup water.
I think I'll try it next time. Also, the recipe calls for 5 quarts of popped popcorn. I used 2/3 cup unpopped kernels and ended up making enough to fill my largest mixing bowl twice. It was an adequate amount to combine with the caramel glaze. As far as a shallow baking dish, I used two 9x13 dishes and they worked fine.