The red forms of cordyline are not so hardy as the more common green form. They can suffer from breezes, never mind the wind. You will no doubt need to protect from the winter by fleece, but better digging them up and potting them in a frost and wind free location. I 'had' one growing infront of hedge that protected it from the north and west winds. It was also protected by the crown of an acer, all the other fairly tender perennials survived, but alas my cordyline died off, new growth always springs up from the base every late spring, but doesn't make enough growth before the autumn. so I tend to treat it as a small annual.