I went one step further and built a custom 2 x 10" sub box plus Amp in the boot. a bit dodgy using just a jigsaw, but i covered it in similar carpet to the wagon and it looks like a bought one. I had pics on here of it, but they've gone walkabouts, i'll get some new ones.
I didn't lose too much boot space, and it fits under the lugage cover, so no crims can spot it.