you will still have the cancellation cause the waves will be different. Putting the 10's in the cab is also a bad idea. I dont understand all the physics about it but basicly the soundwaves will move both forward and back. Again this will cause the signals to cancel themselves out. Also adding polyfil(insullation) will cause the 10's tto 'see' an even larger box. This 'larger box' will cause the 10's be become more boomy and less crisp.