Bongo Fury

Hi there, I welded up a couple of rust holes in the sills today of my (t)rusty bongo...noticed that moisture was coming out of the drain holes/bungs on the sills. Is their anyway that moisture can get into the sills other than the holes I have just mentioned? Was wondering if the front wheelarch rots behind the mudflap, as the biggest hole was in the sill was at right at the front, where the sill ends. Thanks in advance.

Pretty sure moisture can get in from the front wheel wells, when I took out my rear heater gubbins, there was water & rust inside the bong on the upper side of the cill, I could see patches of daylight looking through to the front using my cameraphone.