I tried the coiled tubing in an ice chest method once, years ago, and all the ice melted in 24 hours. Not very practical IMO. One thing I've always wanted to try though just for the hell of it is to pick up a used mini fridge for cheap and modify it into a chiller. A controller would still have to be incorporated though, and with my current tank, I've never had overheating issues so I've never bothered to try this.