In my vintage car I have run IB for years, never had an enclosure. I originally used a pair of inexpensive 12's, now I use four 10's. Very easy to end up too bottom heavy, I do recommend a Qts around 0.5 and Fs anywhere from 30-40Hz. I try to get my response curve as close as I can without equalization, and I have yet to need much power to get results. You will want good soft parts and plenty of excursion, but thermal power handling is seldom an issue. And you will love having no box in your trunk!