Probably not the best advice. I have a weatherbeeta coat (extensively modified by me) which i only use on my boy in warmer months. They are a big square shape, like a horse blanket, and quite stiff, so don't fit the curves of whippets (see Mumtoshelley's pic). Besides not covering the rear end, there is no covering under the chest. I would think in the ACT your dog would need as much protection from the cold as he can get.
My guy has 2 whippetwear coats which keep him warm on camping trips, as well as day-to day. He has peed on them at times, but I would rather that than a cold whippet.
Good luck in sorting your coat issues. :)