Forfarian: Thanks for the photos. The one on Eilean Hoan confirms what I suspected, namely that there was enough shelter for a shepherd to be safe overnight if stuck as my uncle was.
"Sainach" is indeed unusual. It appears once only in Hew Morison's transcript of the parish record, and there is no similar Gaelic word that would make sense in the context of a patronymic. Without looking at the original handwritten record, I would note that Margaret Sutherland is also referred to in the parish records as "MacKenzie", and wonder if it's a misreading of nin Coineach = daughter of Kenneth