What ages of kids do you have? A pretty narrow booster if you have older kids is the Graco Turbobooster. I have a Jeep Grand Cherokee, and can easily fit a Britax Decathlong RF, a Graco CarGo FF, and a Graco Turbobooster back there. The CarGo is crappy as a booster, but as a regular FF seat it is pretty narrow, though it does not have as tall slots as a Radian, and only goes to 40 lb with the harness, plus it is FF only. So if you need a cheaper FF seat for a kid between 30-40 lb that is not too tall, it is pretty narrow and does the job.