My wife and I were quite comfortable camping in Iceland in 1974.
It was late June, and we had good Icelandic sweaters, mittens, and hats, plus down parkas, and long rain shells.
Actually, in Akureyri we had a heat wave. A couple of days with truly summer-like temperatures, blue skies, and sunshine.
But the weather all the rest of our three weeks was photographically exciting, even in the rain.