As said before, the belly cover is NOT water tight. Had the same thing happen after driving through a heavy storm, but only from the part under the basement. I found the problem is the lightweight aluminum strips Keystone uses to hold the coroplast up - it's too flexible. I replaced the front section with U channel from Lowe's and added some clear caulk. Water can still get in back further, but that's resolved the gallons of it in the front.
__________________
|