Classic Motorhome side moulding trim..
My 345, like others has 2 extruded aluminum mouldings, that run pretty much the whole way around...
The gap is where the moulding is riveted on.
On mine the gap/groove is painted black(sloppily!), but I saw on one 345 locally that they had a rubber strip in the slot. Looked like or similar to the "Lock Strip/moulding" that older windshields have. Like a D shape.
I have looked at tons of pics today, and some clearly have nothing in the gap, and some I cant see...
Should it have a rubber piece in there?