I been waiting for a Bose Estate Sub box for ages now, so I can complete my Bose / Colour Screen project on my MV6 Estate, pretty much given up now, there like Hen's Teeth and when they do come up on Flebay far too much money, he's a link and Pic of one that was on eBay recently (£200 inc P&P, Basically paying for a single Bose speaker in a Plastic Box as all the other stuff is readily available especially from Saloons).
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&rd=1&item=190183526017&ssPageName=STRK:MEWA:IT&ih=009I'll probably go down the route of fitting two Saloon Subs in my rear Door with a wooden baffle and lots silicon sealant.
Another idea I had was to copy Mazda, they have a Bose Sub Box that fits inside the spare wheel in the Back, suppose if you remove the steel threaded rod and are good at woodwork you could come up with something?
If your thinking Alpine Set Up, I have a Alpine Media C800R foldout 7" and N077PS DVD Sat Nav which I'll probably sell soon, it was heading for my Cossie, but have decided against it for security reasons.
Chris.