Another thing you might want to look at is the spare wheel compartment.

Years ago, I drove through knee-high water and had inadvertently filled the spare tire compartment with water. The drain plug had clogged up with dirt, so the water wasn't able to drain out of the back of the car. I was driving around and hearing a lot of water sloshing around in the back whenever I'd accelerate or come to a stop.

(I could've actually filled the back with goldfish and started a little aquarium! How nice! :D )