[novok]

I personally don't have a kid or know of one with ASD, but I was putting a bunch of previous info in my head plus what you describe as a potential solution. AFAIK ASD often comes with sensory processing issues, within and without as you described.

So by putting someone in nature, which can be sensorily calming for some, along with the social expectations and such, and nature being known to help people's sleep I would put it all together with what I suggested.

For me it would more be a debugging thing. Like if sleep in nature worked, then that is a hint, if it didn't and an indoor equivalent didn't work, since for some the nature stuff can be anxiety provoking for other reasons, then it's something else, etc.