Hmmm... Let me try describing this part again -- it seems like a general design element of the TM, I would think most of these trailers have this strip, on the outside of the roof shell right below the front (tongue) window.
At the front of the trailer, on the raised shell, is a trim strip, probably metal, about 4"-5" wide, which I suspect is placed to protect the trailer shell material underneath from debris thrown from your tow vehicle when the trailer is collapsed. With the rub strip gone, I can see the metal trim is applied on top of the shell, so there is a very slight (say .1"
lip.
The rub strip is about 1" wide, and it covers this seam at the top of the metal panel. On my 2720, the strip is one piece extending from one side of the trailer to the other.
My guess is the TM factory adds this metal strip, then applies a similarly thick piece of double sided foam tape on the shell material at the top edge of the metal strip. The 1" rub strip goes on the foam tape.
I think I'll try the silicone caulk on Friday morning before I finish loading the camper for the trip.
BTW, everything else seems just fine after the few months stored!
Jon