So an interesting post script to this. That middle bike rack faces backwards, which means there is a nice long flat bit that sits directly above an open sunroof. Had some rain the other night, followed by a beautiful morning, so family loaded in the car, sun roof open and off we go. First hard stop and the water that (unbeknown to me) had settled in bike rack overnight came pouring in through the sunroof. Freak out ensued, but thankfully (by incredible luck) the water ran straight into the (thankfully empty) cup holders where it was easily mopped up.
Anyway, lesson learned! Oh, and its also a heck of a lot noisier up there with the roof open!