I am also very likely to be related, but am first-generation removed from Caithness. I have traced back to early 1800s for sure, with a probable link to 1779. All were living in Caithness, but not sure how they arrived there. Most earlier links about McPhees prior to late 1700s were in the Western Isles or thereabouts. We can only speculate, but the 50 yrs after the battle of Cullodden were times people in power in the region should be deeply ashamed of with the Highland Clearances etc, so perhaps the McPhees were displaced and forced further north and living hand to mouth. For whatever reason, pride, dispute, choice and want for freedom? the lifestyle continued. I don't know. After the second world war, the family were shifted into housing or put up in caravans.
Another person responded to your post by adding a link to a book chapter. I've seen that book chapter before. While there's no doubt that the families were living an unconventional and very tough lifestyle, i think that it's very unlikely that they'd be walking around naked. Just think about how cold it gets up there, and cutting past the very crude/tough language there is a prudish undertone, at least in my family. The writer has also clearly embellished in the final paragraph on p64 (71), choosing to ignore the accounts of oral history and instead creating tales of slum dwellers.