Which plastic wrap is okay for oven use?
The plastic actually does not reach 300°F in the oven.

According to a forum post at Cheftalk, the dish beneath the plastic releases steam, which cools the saran wrap to 212° F, which is still below the melting point.

However, you should not just use saran wrap. Saran wrap easily shreds, and there are special foils for heating food which are usually refered to as reynolon. These are stronger and more resistant against releasing chemicals into the food. Check the forum thread above for more information.