Hi Gun Smoke;
Welcome to the forum.
I've never smoked oysters, but have smoked other things that require a pan. When using a pan, make sure that it is small enough so that it doesn't cover the whole rack, and it has short sides. The pans I use are 10.81-inches x 8.44-inches (measured at the bottom), and about 2-inches high. I get them from BJs, but I'm sure you can find similar size pans at Wal-Mart, or you local grocery store.