I'm using the black fortex tubs this years also. I do have electric in one coop, and keep the bowl near the light, but doesn't keep it from freezing. I'll just be glad to be able to flex the ice out easily, and I'm thinking the rubber might help insulate a bit. In my smaller coop, with 4 birds, and no electricity, I bought a size smaller fortex bowl, but they have been prone to tipping it over, so next week, I'm going to go buy one more larger bowl, put the smaller one in it, and I'm hoping this will eliminate the tipping over, and maybe offer a bit more insulation.
I don't think, without having electricity and heated bowls, that if the temperature gets down in the teens, that there is any foolproof way to keep water from totally freezing. I would think though, that if you can give them fresh water twice daily, they should probably be fine.