Scott,
Have you tried out that "Woox" sub from Kenwood? It is a tiny, low profile unit that might fit without mods in the emergency kit compartment. I don't need to wake up the neighborhood with thumps that register greater than 2 on the richter scale and I thought this might just fit the bill.
Alon,
Er, uh, the unit of capacitance is the Farad in honor of Michael Faraday and not the ferret in last year's Budweiser commercial
. (Makes you kinda lose credibility you know, and I know that you are a pretty knowledgeable guy.)