Yeah, they're getting bigger aren't they, folks were very happy with a 28" once upon a time.
For large sets I use MDF board specially kept for the purpose..... if ever you scrap a largish telly, have a shufty in the screen..... you may find a nice thick rigid plastic sheet.
It's not just a matter of supporting, all you need is a blob of solder or grit underneath and it'll leave quite noticeable marks, geesh, the ol crt telly's, folks use go over the cabinet looking for the slightest scratches...... er worm hole.
Dave