I agree, it sure as heck seems like some kind of "infant mortality" electrical/electronic issue, awesomeman: but these things sometimes defy logic IMHO.
As you know it is recommended to start the Onan once a month and run it under 1/2 load or more for 30 min to an hour (the load application is to drive moisture out of the generator windings etc, primarily). Hard to believe that 60 days would cause varnishing in the carb, but just for grins: What do you think about removing the air filter; spraying in a bit of starter fluid, and than see if it will at least "pop"? Also, even though your coach batteries are up to snuff, you might start the big engine and let it put a little more "umph" into the coach batteries (automatically via the boost solenoid ..... just as when driving.) I know mine sounds like the Onan starter spins just a teensy bit faster when the Ford is running.
I guess if the above doesn't get at least a "pop", you might pull the spark plug and see if the points are clear ...... and maybe just replace it (cheap).
Good luck and keep us posted, please. We are all "still learnin' ".
Safe travels........... ed s