"ShrimpBurrito" has completely removed those plastic strips and carefully re-applied new ones from the factory using NO caulk. He describes the procedure on the forum somewhere.
But the strips on our trailer came from the factory with caulk applied, and like you, we had leaks, which I've described over in the Elkmont sub-forum. I fixed them by stripping out the old caulk and applying some new G.E. Silicone II external caulk.
Just yesterday I noticed another small leak and checked out the roof. Sure enough, there was one small section of original factory caulk that had pulled away from those &^%$ plastic strips. Not sure why I didn't replace it before, but I have now.
As before, the gap was between the strip and the caulk, not at the Al skin. I've posted pictures of the original caulk and the gap here:
http://picasaweb.google.ca/lh/photo/...eat=directlink and here
http://picasaweb.google.ca/lh/photo/...eat=directlink