I did it a year and a half ago. It was drinkable and actually not too sour...
Here is the link to a write up I made about it:
http://www.brewnosers.org/forums/viewtopic.php?f=3&t=2216
I've had success with putting a carboy (or bucket in your case) in a rubbermaid plastic container filled with water. I wrapped everything with two sleeping bags to provide some insulation. By adding 4 L of ice in the morning and 4 L of ice in the evening I kept my system about 10 degC below...