Hi,
Not sure how practical a fixed fold-down tv would be, you’d need power and aerial cables to ran under the pop top mattress which could be done but when you raise the bed up the tv would be very high up.
Have you thought about using a tablet/iPad with a movable mounting arm (easier if bed board isn’t lined, use a suction cup)? You can get tv antenna plug in modules to watch live tv if you don’t have Wi-Fi available on the van.
i seen this on a knights camper conversion, there’s a video showing it, looks pretty slick.
When the roof bed is up you could simply move the mount arm elsewhere.