RE the tubes. In the array the tubes are also part of the structure of the system, and its essentially that they be very rigid, so PVC tubes work best. They are also visible.But since I'm also building the woofers using sonotubes and those are essentially pressed cardboard about 1/8 inch thick. They'll have a mdf and hardwood top and bottom looking like a greek pedestal. I'll be using a series of MDF pieces sliced and glued together with a hole cut in the center for the woofers.
Marlboro