J.F.
Don't know if this will work, but my first thought was baking soda (similar to the kitty litter). You might consider buying a big box (or two) and either
*sprinkle the seats and floors with it, letting it sit for a bit and then vacuum up
or
*pour into pans (like the kitty litter) and let it sit around for a few days
I know the smell and wish I had the wisdom I do now, back in the day. I "cleaned" out my old beater of a car when I was in high school with a garden hose!!! Did I say that I know the smell???? LOL!
Good luck!