Does the set have a built-in app to play video? I mean I'd expect it does, and doesn't it have a loop mode? If not, maybe add an app with loop mode?
On mine, the loop mode is not seamless, there's maybe a couple seconds delay, but that might be acceptable if you create a video file where it is already looping for hours (same footage repeating within the single video file you create) then when the TV reaches end of file, there is only that short hesitation till it loops, starts back at the beginning of the file and plays for hours through the file again.
If that seems viable, then need to find what the video playback limitations of the TV are, for example max file size, or size of USB flash drive to store it so no need to stream from a host, instead TV is independent and reading from its own USB port.
If worried about someone stealing the USB flash drive, then I'd just get a few cheap ones. A multi-pack of 32GB are around $5 per.