Well, it was worth a try, but the DPST switch did not fix the problem
either. It worked fine for about two weeks, then tripped again a
couple of days ago.

Please describe how you wired the DPST switch; post a diagram if
possible.

As you would expect. The incoming hot wire goes to one pole of the switch,
the incoming neutral wire goes to the other pole. Then the switched hot and
neutral go directly to the fan.

The ground wire is directly tied to all other grounds.

The switch clearly indicates which two terminals are the "line" and which
two terminals are the "load". Outgoing hot wire is on the same pole as the
incoming hot wire, and the outgoing neutral is on the same pole as the
incoming neutral.

I don't see any other way you could wire the switch?

Anthony