Those pioneer subs are pretty cool for very shallow enclosures, but I'm not sure you'd really need them for the rear door of the VX. Notice that the recommended enclosure size isn't much smaller than most 12" subs (about .8 of a cubic foot - my Orion's are sealed in 1.0 cubic foot). I don't think depth is really a big issue, even for those enclosures built inside the spare donut tire. Of course, I've never listened to them so they might sound great, but my guess is you'd be better off with a traditional full-depth sub like an Orion or a JL Audio.