Not sure if the following will help you, but....
This is my latest attempt to cool a beer tower. Its a computer case blower fan. I took an end cap for the PVC tube I was using, cut a slot in it and glued it on, and ran my hoses through a different set of holes. Not 100% sure it will work, as the tower is sealed and I'm sure has a tremendous amount of back pressure, but we'll see.
I bet if I ran copper snug against the lines like this the lines would stay very cold.... hmmmm