Rear Bump Tray Collecting Water

I had my 2008 Classic 25fb parked outside the house and a heavy thunderstorm passed through. Later I noticed the bumper tray had pooled some water. Is this from water entering through the tray opening? Are there any tips for sealing it better? I lifted the vinyl matt out and the tray had a large white corrosion spot. What's best to clean the white corrosion. Should I coat the inside of the tray and not use the vinyl line?



Thanks



Kelvin