Here is Patrick Sun's website on his Sonotubes. He is that master at them and has very detailed instructions with pictures of all his projects. These are for large home theater subs, but you can just scale it down.
Stormin' Norman 2000 SVT 17" AT Italia Spa w/ Kumho 215/45-17 VCN-2000 Eibach Springs Bassani Best #'s so far- 268.5HP and 275.8 ft-lbs at the wheels #463/2150
