Aren't those gutter extensions much larger than our gutters?
I have a '63 Overlander and I have the same issue. 1963
was the year they ended the gutter right at the window end, thus all of the water runs right down the rivets. They smartened up the next year and made the gutter extend out an inch more!
To make matters worse, it's the one area that you can' t get at to seal from the inside of the trailer even while doing a shell off.
Let me know it you find something that fits. Otherwise I'm going to have to fabricate some
Rain chains would be a mistake, good stiff wind and they'd scratch!