I am now sufficiently interested to look deeper at this; I originally went for the open speaker approach based on Doug's descriptions and experiences, and yes, when I tried it, it appeared to make a difference. It was also due to the fact that there are no real locations inside the cabin of a Mini to place an enclosed bass unit of sufficient volume.

What I would like to do is design and build an enclosure from damped marine plywood to a custom shape to fit in to one of the few locations I can place the woofer. So, have you got any URLs or reference materials on the design of bass unit enclosures?