I’ve had this car for about a year now and recently it seems that the floor behind the passenger seat gets wet whenever it rains. I’ve look closely and felt around the seams by the doors/windows and it doesn’t seem that it is coming in from there. It seems to be the wettest around where the passenger seat is bolted to the floor…I’m not sure if this is because that’s the low point or if maybe it’s coming in from there?
Matt, Are You Out Of Bumper-To-Bumper Warranty ? Does The Car Have A Sunroof ?
Your theory of water running to and settling in a low spot is a good one. That can be a different location than the source of the leak.
On some 08 Avengers w/sunroofs kinks have been found in the rear sunroof drains, just behind the wheel wells in the trunk (possibly behind a trunk lining). This situation causes water to back up, leak, and accumulate on the car’s floor. Sunroofs leak water by design and it needs to be drained away to the outside.
The fix is to install lengths of convoluted tubing (slit open) over the roof drain tubing to keep it from kinking. You’ll need two lengths of (can use Chrysler part #HCT00374AA), 1/2" convoluted tubing cut to about 10" lengths to make the fix on both sides. Start the tubing at the clamp on the car’s drain tubing and go down from there, slipping the new part over it.
CSA
Bumper to bumper warranty is gone 
I don’t have a sun roof, but I think you are on to something with the water collecting somewhere and leaking in. There seems to be a lot of water that collects in the space where the water from the back window falls into under the seams of the trunk lid and also where the water falls of the windshield underneath the hood. It’s like its designed to channel somewhere but it’s too flat and ends up just sitting there.
Matt, Rear Antenna ?
CSA
I’ve got an antenna on the middle back of the roof.
I Wonder If That’s A Possible Source Of The Leak ? Sometimes When An Antenna Leaks The Water Follows The (Lead) Wire And Drips Off At A Low Point Or Bend In The Lead.
CSA
So, I have a 2014 Avenger and I’m experiencing the same type of issue. I sat in my car while it was pouring yesterday and saw as the water rose up from the bottom and collected behind the passenger seat on the floor. What was your ultimate solution to your problem? I hope you get this reply. I’m at work now but I’m definitely going to check for debris build up in the drains under my trunk lid. Also, I have no sun roof either.