Heck, I've got a 4-door and found that I couldn't put my son's rear-facing seat behind me without pushing the drivers seat up to the point that it was uncomfortable. Ended up putting him on the passenger side until he was big enough for a forward-facing seat.
Of course, you could always opt for a car seat with a smaller footprint. We had a Peg Perego Primo (something-or-another) when our daughter was born. That one was MUCH smaller than the average Graco, Cosco, etc that you see everywhere.