Everything that has been said - plus a heat gun or hd hair drier helps. Temporarily install the rear seat and mark a chalk line where the base crosses the floor, the carpet must extend that far. Sit in the back seat and look at the firewall showing under the dash, make another chalk line. If possible cover this line as well. The only real trick spot is at the outboard corners of the rear bench. There is a triangular spot that you will probably need to sew in a piece of scrap carpet. Try to end up with a couple pieces of scrap big enough for the sides of the console (if you have one). I don't remember if your car has a console/floor shift.