Ok, but the flood is in the backseat footwell. If water coming from the firewall, the front footwell would be wet too. I couldn't quite make sense of it. I looked under the car and the floors were solid.Or the firewall is rotted above the HVAC box, or the cowl seams are leaking. All common scenarios,, even in TX cars.
I could even work with the doors. I would chip the loose rust and pickle it and spray paint it. It wasn't a situation where you could insert your hand or anything. Trunk looks great too. Here's more pics.