I've found main GFIs to be a problem precisely because it can be so difficult to track down the fault sometimes.
It sounds as though it could have been a combination of leakage in various places due to the rain getting in. You can find that each circuit turned on individually, or maybe a combination of two or more circuits doesn't cause the GFI to trip, but turn them all on and the combined leakage exceeds the trip threshold.
The part about putting the freezer up on rubber mats stopping the GFI from tripping sounds curious, almost as if the freezer casing wasn't properly grounded.
[This message has been edited by pauluk (edited 08-05-2002).]
