Just took the unit out of hibernation and, in short, my mod worked...and, I might add, very well.
The awning was dry after its winter nap, no new mold spots and, as a bonus no black streaks from the roof (though interestingly, had black streaks ON the mod, but since the water was directed over the trailer awning, nothing on that side of the trailer).
For those of you in those hot, dry and sunny areas (as opposed to northeastern Indiana), this also may be a good mod to prevent sun damage to your awnings. Of course, if your awning is wider than 10', you'll have to add a second length of rain gutter. I suspect those could be joined using PVC cement and or pop rivets...chewing gum, not so much.