Did you ever find the source of your water leak. On the 2005 and later trucks, I doubt if it can be the A/C condensate problem that older Dakotas experienced. Ours has a hard plastic, oval shaped drain that is protected/obscured by a metal heat shield.
I did find that the cargo/brake light assembly had the gasket partially tucked inside the opening and was letting water run in and down the side and along the floor.
I too suspect a leak in the passenger kick-panel area, but haven't located it.
Has anyone solved this problem?