'Clan Gunn castles' are really Gunn fortalices
'Clan Gunn castles' are not castles - they are, at best, fortalices (fortified houses) due to their size.
Glensanda 'Castle' (Morvern) is classified as a Tower House by the RCAHMS; NIgel Tranter page 178 in Volume 5 of his 'The Fortified House in Scotland' which covers Caithness and Sutherland, views Glen Sanda as a fortalice. And the supposed 'Clan Gunn castles' are roughly the size (or smaller) of Glen Sanda, one being 37 feet by 23 feet, the other 44 feet by 28 feet.
The word castle has been lazily applied to a fortalice; the use of castle supports a vainglorious view of Gunn history.