if anyone has a dribble of water coming down in the passenger side corner of the floor, this might be your culprit. you must pull the hvac to get at it.
I think this truck suffered from every single possible water leak save for a sunroof (but only because it doesn't have one). the good news is that it's a southern truck and the rust up in that corner is just surface and can be dealt with without welding. there is a patch needed on the floor though.
these are just the ones I found on the pass side