Pesky leak

I have a leak at the front of my trailer that I have been chasing for some time without much luck. I can see it on the floor right underneath the roadside battery box.



I thought it was the caulking above the panorama window - fixed that - still leaking. Then I thought it was the caulking around the battery boxes, fixed that - still leaking. Next I wondered if it was the window seals and I taped those as a test and it still leaked.



I really think it's the battery box so two days ago I decided to take out the door for the battery box to see what was going on. The PO must have had it off because the rivets are gone and there are stainless screws instead. So I got it off, cleaned up the edges a bit where he had used silicone between the box and the body (grrrr) and put it back on. The perimeter is sealed with Parbond too. Yesterday I go out and it's leaking far worse than before I took it off. There was even water on the top of the box.



I'm now wondering if the screws could be the problem and water could be traveling along the threads into the wall. Should I replace those with Olympic rivets? Anyone else experienced this?