How hot does the oven get? How hot does the light get?
Worst case scenario is that they burn a little and don't look as sharp. It would be hard to make the pie tin melt or do anything dangerous.
They will be used for one 2 hour show (okay we'll say 3 hrs to be safe).
I've never thought of comparing the lights to an oven before... Makes a lot of sense.
Are they going to be on for the entire show?
For what it's worth....
I did a show recently that used about a dozen foil pan gobos. Rarely were all on at once, most would be up for 5-10 minutes at a time, usually at 100%. All were in Source-4's at 575w, pointed straight down. Show ran 8 shows a week for 2 months. When I took them out they were like new, you'd never know they'd been anywhere but sitting on my desk the whole time.
Similarly, a couple years back I had a set of 6 foil pan gobos which were very titchy shapes; they were in Source-4's, again at 575w, focused horizontally. These ran fairly steadily for about 30 minutes each before getting to cool, in the 65-85% range. 8 shows a week for about 2 months. And again, at the end of the run, no burning, no curling, no nothing.
Get the heavy aluminum cookie sheets, thick like foil turkey roasting pans are made from.