We have a 2006 Prius and are in the market for a new convertible infant-toddler car seat for our 7-month-old son, who will soon outgrow his Graco SnugRide infant seat. I can get a special deal on Britax seats through work, and I've heard such great things about them, so I definitely want to get one of those - and I'd prefer to get one of the larger ones (Marathon, Decathlon, Boulevard) because they'll accommodate my son until he's 65 pounds. But I worry that these seats are so big that they won't fit REAR-FACING in the backseat of my Prius without making me or my passenger have to sit fully upright in the front seats! I know I won't have a problem once I can switch him around to forward-facing, but that's not for another 6 months or so. Until then, I'd like us to be able to sit comfortably in the front seats! So...long question short...do the Marathon/Decathlon/Boulevard seats fit well REAR-FACING? Any and all advice/experience regarding where to install these seats (behind passenger seat or in center back) would be great too! Thanks!