I had a sub in my i-MiEV for the two years I leased it. I just used a standard 10" sub enclosure (non-ported), a 10" Pioneer sub I had sitting around, and an older Sony amp that accepts speaker-level inputs. Just tap into one of the speakers for the input. For power, find a large fuse and tap into that for the switched and unswitched power. Worked like a charm for me and only took me 15 minutes to remove.