Rear doors are usually problems due to the design AND they rarely get used so water will not easily moved to help drain out of the door.
Also the doors being used more often may also keep the butyl more flexible??
If your car is parked in the summer and has condensation build up after sitting, you have a moisture problem somewhere.
Could with with AC drain, sunroof, door vapor barriers, also check the trunk and the rear fender wheel wells, poorly sealed replacement front or rear windshield can also be an issue.
You may not be able to feel the damp carpet, because the moisture may end up on the jute backing if the problem is in the cabin or front of the car.
Trust me, you have a moisture