My X3 is due in next week and I purchased the cover r6girl mentioned. We'll see how it works. I have a 125 pound Great Pyranees and a 166 pound Great Dane. They had better fit. :-)

I'm actually not that worried though. I have an Explorer Sport Trac right now with a very small rear area and they fit for short trips. They're gonna love the extra space when the seats are folded down!