I've been reading through your SQ thread and have been evaluating different options - - although the slightly above zero weather isn't encouraging me much.

I also need my trunk space pretty regularly, and have no intention of dropping $1000 on that sub that mounts in the left corner of the trunk. (doesn't have very good reviews anyway)
Since there are many like you, I've designed a subwoofer kit that requires very little space but provides more than adequate sub-bass support in the form of an 8" high-excursion subwoofer. This subwoofer requires about 0.35 cubic feet of internal space, allowing for a very small design that would occupy less space than a child's backpack. It is by no means an "SPL" subwoofer, but will adequately produce deep, musical bass notes. The kit including the amplifier, subwoofer, and subwoofer box would cost around $400 (give or take $25 depending on design), which is significantly less than the OEM options out there at this time while providing vastly better sound quality.
Should you need additional output, two of them can be used and still occupy only 0.7 cubic feet, or about the size of a normal backpack, although at this point you may be paying a premium simply for the space savings of the particular drivers. They would have output comparable to somewhere between a single 10" and a single 12" subwoofer and would come in at around $440
not including the amplifier. A suitable amplifier would cost around $150.
There are many options that I can give you that will depend on your system goals and your budget. All you need to do is ask.
As for it being cold right now, that shouldn't be of too much concern as I wouldn't be able to have any new orders built for at least another 1.5-2 months. Most people don't find this to be a problem as they are willing to wait for a very high quality product that is built by hand with great attention to detail.