I will use some sort of Ziplocs or trash bags or something from now on! It sounds like this really does happen all the time.
The camera manual is just matte finish paper. It is still a little damp, but I think he will be able to use it. The pages don't seem to be sticking together. It is a little "crispy" so I will mention the iron to DH.
The situation was not like the bags were being loaded when the storm hit. We could see this wall of BLACK clouds and lightning coming well in advance. There was no plane at the gate. A plane landed as the rain and lightning started, but they left it on the tarmac for over an hour until the rain stopped. At that time they chose to send that plane to Dayton, not Dallas. Those passengers were already stacked up at the same gate where we were, and that flight had replaced ours on the board. No idea where their luggage was at that point. I suspect ours was out in the rain!
The next plane at the gate was sent to Atlanta, despite our flight being put back on the board. They moved us to another gate to load us on a plane that they had diverted to Tampa in the thick of the storm.
I certainly don't want anyone to risk being hit by lightning. My thought is more that our luggage shouldn't have gone out in the rain, because they didn't have a place to put it once it got out there. The e-mail I got stated that the luggage carts are covered, but this was obviously not just incidental exposure to the rain.

I am guessing they pulled the cart out in anticipation of loading the luggage for our scheduled departure, then the weather turned and the ground crew went inside without covering the bags. It seems like they would have had enough advance warning to move the cart or cover the bags, but maybe not.
I don't think this was caused by liquid in someone else's bag. From the way our bags came out, I would say the 2 really wet ones were flat on top of a stack and took the brunt of the rain for a sustained period. The bags were uniformly wet, and the water penetrated down into the bags like rain would filter down into the ground.
I am hopeful that SW will honor the AirTran credit. If not, well, lesson learned that the airlines can and will leave bags in the torrential rain! Next time I will be ready!