Chuck, the panels will be placed permanently on the roof with tilt bars for Winter. I will place all four of them so the center point of all four is in line with the vent cap. This is to use the shortest amount of wire possible, but I will make sure they are far enough appart so as to not shade another panel when tilted.
As far as running the wire down the side of the vent pipe, quite frankly that scares me to drill a hole in the roof without knowing where it goes. I tried to shine a light up the pipe side from the basement but it looked like the pipe was touching against the wall as it went up. In other words it just didn't appear to be a clean open channel next to the pipe which concerned me that it would be drilling a long way before seeing any open space. The idea of using the vent pipe is not mine, you can see the approach in the article the "12 Volt Side of Life" http://bart.ccis.com/home/mnemeth/12volt/12volta.htm
Thanks again, John