Interior water leak

I have a 1999 Chevrolet 4 DR Blazer 2WD that when sitting still does not leak during rain events. When I drive it during heavy rain events it takes on water in the passenger rear floor area. I have replaced door weatherstripping on both front and rear doors as well as checked to ensure drain in bottom of door panel is not obstructed. Sitting in the vehicle facing the passenger rear door the water appears to be coming in at or near right rear area of the floor near the wheel well and at the bottom left near the middle door post. It seams to be getting in between the floor panels and blowing back. Have looked underneath and attempted to seal all open seams with frame sealer and undercoating. Any ideas?
Vulcanwayne