On the front and rear wall near the bottom, does yours have the little plastic eaves troughs glued in place to act as drains? To the inside exterior surface, of the front and back wall, is there an Aluminum Angle iron attached to the wall. This would be located behind the rubber vertical slide seal. If so, this is not sealed to the wall. If water gets behind the slide seals either on the top or ends of the slide, it will wick between the angle and the wall and get to the bottom and the carpet. Our 01 Ambassador had the same design slide. I ran a bed of sealer between the wall and the angle and cured the situation.
Hope this may help, Happy trails Bert