You could try to address the influx of water. There's two theories on how water gets in; bad grommet or the water gets inside the plastic shielding around the wiring near the battery and water then runs all the way back to inside the car.

Even though I've never had this problem, but warned of it, I applied fixes that will hopefully seal both pathways. To obtain access to the grommet remove the fender liner.

 

Yea definitely like Barney said, address any and all water getting in and traveling down that harness and you'll never have corrosion at the connector junction block!!