for ease of mounting, the only other spots would be the A-pillars or the kicks panels i think...going with a midrange, i'm hoping to mitigate some of the reflections caused by the tweeter's wide dispersion. i realllllly dont want to deal with the windshield. bateman balls...
reversing the polarity (flipping the wave) should cause some cancellation, if its at 180 degrees to the other speaker...i think...