Say if I wanted to add some bass to a motorcycle.

Thus - no wall/corner loading. No benefits of it being inside anything except open space.

To get at least a some what flat response (if possible at all) without sounding too boomy, what would be my best bet for enclosure design (alignment/Q or if going ported, what to tune to and how big to go?)

Say for example if I was using a average 12" woofer that would, in car, would need the usual 1 cube sealed, 1.75 ported.

Has anyone ever designed something like this for use outside a vehicle?