Mormit: While I have not had the pleasure of installing a system in a wagon (yet), I have done so in other vehicles, including a kick-ash system in an MGB of all things! To answer the larger question, however, you are correct that only ONE sub is needed. Bass tones are non-directional as percieved by the brain. This is why any home theater/stereo system worth its salt has only one sub. Any car audio store that tells you that two is better (or even needed) is just taking your money, or has a sales staff working on commission. Stick with one. You won't be disappointed. Just make sure your R-L and F-R are biased properly on the rest of the speakers, and don't forget that you need to phase all the speakers equally, otherwise your sound will be muddy.

Brad