Shape will have no effect in a sealed enclosure. There's a common misconception about standing waves in them and cancellation, but the enclosure will simply never be large enough due to the wavelength of the subbass frequencies. If you do get an enclosure large enough, then you're beyond the point of having an enclosure.
They can have an effect on air movement within a vented enclosure, but I am not sure on the specifics, and it's best described by some physics, which I **** at.
If you have the time and money, experiment with different shapes so you can gain some first hand experience.