Yes it will work, no you won't get cancellation. The general rule is that as long as the speakers are spaced within 1/2 wavelength you will get some form of constructive interference, the closer the better (at 1/2 wavelength the positive cycle of one speaker is being cancelled by the negative cycle of the other speaker). As an example, at 80hz the wavelength is about 14ft, so you would want to keep path-length difference between you and each sub less than 7 feet. As you get lower in frequencies the allowable PLD becomes larger because the wavelengths are longer, so it's fair to say that it's going to be really difficult to get true wave cancellation at bass frequencies in a car.
There will definitely be an effect on the overall modal response though. I doubt it will be detrimental.
edit: I didn't read that this was going in a truck; I though this was in a car trunk. If that's the case then you might have issues. Truck cabs are almost like tiny cubes and tend to get weird modal issues.