I've always done it. I have water troughs like this: http://www.horsesense-nc.com/Images/raintrough.jpg
But mine are blue.
The fish do well even in the summer (Cali - 115 degrees), they just hang out at the bottom. Just make sure you keep the water level filled up. In the winter, we brought them in cause the troughs were starting to freeze over and I kid you not the fishies were about frozen solid. They didn't move and when you tried to bend them they were pretty tough. Put them in some cold water and they popped back to life LOL
They do get VERY big, and it seems they grow really fast, being in the troughs.