I do have some experience with the elusive "under door leak" that seems to leak from under the floor mats. The week before I picked up my 2014 JK it had rained heavily for a week. sure enough, the driver's side floor was wet under the floor mat. Passenger side was completely dry. Now, i ordered my Jeep from the factory, so it wasn't like I could just pick another one off of the lot.
Having gone through this experience on my 2012 without satisfactory resolution, I was concerned. But, I also know the passenger side leak could have many causes, hence the "elusive" part. Driver's side seems to have a straight forward, easier resolution from what I've read over the past two years on these forum pages.
So, those of you with DRIVER'S side leaks, I recommend that you try this. I read about it on the forum and it has worked to COMPLETELY resolve my leak: Door Entry guards. But, you have to install them as illustrated in the picture below:
The trick is to install the entry guards over the front seam. Try it and let me know. Mine is completely bone dry now, even after heavy rain.
BTW some dealers will try to tell you that the entry guards caused your leak, but mine was leaking before guards were ever put on! Good luck!