I am building a hollow book raspberry pi enclosure which has a small screen inside. Do I need to drill holes in the top of the book to allow heat to escape?
I would suggest testing with a temp probe before doing the holes. Also the temperature can have variations depending on so many factors. Do you overclock ? With what material the case is made. Is there airflow around the case ? Anyways the list goes on... Something I can tell you for sure, I tested it myself. A lot of air can go through the USB ports and all the other connectors when those are not all in use. I suggest you use a hub or just a WiFi dongle.