I have a similar setup to yours. My garage has three windows and two garage doors. It is insulated and drywalled with a room above and GFI outlets. I've been brewing in it for years. My basement laundry room is on the wall of the house that the garage is attached to, so from the start I ran a hose from the laundry sink to the garage for chilling. Last year I added a SS mop sink with hot and cold water. The drain line is an open-sight drain into the laundry sink. I had the plumber put cutoff valves on the incoming water in case of cold. I'm in Maryland and the garage hasn't gone below 40F with the windows and doors closed. I don't even try to keep it clean, though, with two cars coming and going. The sink has been great, but might not work in your situation.