I think that you're overthinking this.
I used to own a Mazda MX-6, two door, smaller than your car. I once hauled a calf in the backseat! The looks I got from folks as I was driving up the freeway, were priceless BTW. People took pictures, laughed, gave me strange looks. It was really fun.
Anyway, I used to haul pigs in the trunk of this same car. It will be dark in the trunk, from my experience the piggies just lay down and go to sleep. The temp won't be too bad If you are running your air conditioner, the ambient car air helps cool the trunk. If you are super worried you could crate the pig and fold the back seats down in your car to accommodate the crate.
Or put a harness on your pig and tie her in the back.