Kick panel rust! Help!

[texjake]

Can anyone help me determine where this rust is occurring from on the kick panels? Is water getting in around behind the vents or around the windshield and leaking in & down behind the firewall? I have noticed it every time it rains it's wet there and not sure if its leaking in from in behind or where my leak is coming from. Is this common for most of these truck or do I have a bigger problem than expected. That's the only rust on this truck, the rockers are all solid.