There are some good solutions mentioned here. So far, for my dual twin-tower setup I'm sticking to simple. I have a copper pipe running the interior height of each tower, to provide a clear air channel as well as the metal itself to conduct "cool" into the towers. It's nestled between the shanks at the top and sticks out an inch or two below the ceiling of the fridge, well out of the way of the kegs.
With nearly all setups, lines running up through towers lose their chill the higher and more cut-off they are from the fridge. There shouldn't be a dramatic temperature difference though. Has anyone who is experiencing this problem measured the temperature inside the tower at the top compared to the base/fridge?
Also, what 3/16" ID line length are people using here? For each of my tower taps, I went 10 feet. Even before I added the copper pipe, I was getting no initial foaming. I'm wondering how much line length might be playing a role here.
With warmer beer can come foaming, but temperature alone should not be producing dump-worthy beer. Perhaps there is a microbiological issue with deposits in the lines or with the beer itself that accelerates in the warmer line environment.
Beer in warm lines should taste warm, not off.