Old 4 wheelers trick that I've used a few times, including one that had a gallon of milk ferment, explode, and dry over a week in the summer sun. Place a bowl of ammonia on the floor. Leave the car closed and preferably in the sun. If it's cold, hang a shop light inside to act as a heater. Anything to get it warm inside and evaporate the ammonia. Open the car up and let it air out for a day or two.
I bought a car off a little old lady that put moth balls all over her garage to keep mice away. The car soaked thesmell up. It was strong. I kept it outside and over time with the window sdown it eventually left. I tried everything and kept cleaning the car. It took about a year of use to air it out.
I can vouch for the charcoal method; one big bag opened up and maybe distributed around the car should do it.