Sorry for the run of bad stuff. On the bright side, you already know about where it is in the car, as you said it just blows stench when the floor vents are on. Buy or borrow a repair manual and see how the vents in question are put together. You may even be able to find some of it online. There really isn't anything you can do for the smell until the decay process has run it's course unless you remove the source of the smell. Even bleach won't touch it.