We use them too for our older more fragile ladies but haven't done it this year. Your girls are pretty old though I should think they would appreciate them at night time. We also put one on one of our ewes who had lost condition and we expected her to die and she hasn't so she's had one on for about 2 months. Took it off a couple of days back, her fleece is fine, will put it back on if it gets cold and wet at the same time.
It's nice to know people take good care of their animals.