I know nothing about that particular rig, but from general info, I can suggest a couple things. Since it was raining, it is possible that you have a pending short somewhere in the electrical system, and the water caused arcing. Obviously, the higher the voltage, the more easily this occurs, so I'd start looking at the generator 120 volt lines first. Obviously you have no spark plug wires to worry about, but 12 volt wires could be the problem, too.
The other possibility is the engine air intake sucking in water. I don't know that this rig is prone to the problem, but I have known of people with OTHER diesels that did suffer it until the fixed it. It had to do with the air filter getting soaked with water, thus not passing air and temporarily choking the engine. The fix involved relocating the airbox intake so the wheels didn't splash water into the intake.
Best of luck tracking it down.