Before buying anything new, or putting factory subs back in, or resorting to other extreme measures, try the subwoofer in various locations in the trunk. Move it forward, move it backward, move it from side to side. I can't stress this enough!! Since the waves emitted are of such low frequency and high amplitude, especially in an enclosed space such as a trunk, recombinant wave effects are of the utmost importance! I wish I had an SPL meter to report the difference in results with just moving the subwoofer from up against the back seat 2 feet forward (backward) into the middle of the trunk... the difference is night and day! There is definitely one "sweet spot" in the trunk where the bass will sound the best, regardless of the size or power of the sub. You just have to find it. (I have the factory woofer in place and disconnected, my bass is GREAT with a single JL audio 10".)