If the Regent isn't fitting I don't think an Apex will either, it's a BIG seat. It also requires head restraints/high seat back, it's not reinforced as a stand alone shell, like the Marathon, etc. Which really leaves you with a Radian. You can check on car-seat.org's forums for a list of cars that have had successful installs with the Radian, it can be tricky, but is a good seat once you figure it out.