Gap in window trim?

I believe what you are referring to is a rv window glazing bead. I had bead shrinkage in 2 RVs and manually pulled the rubber bead from the frame (no...the glass window did not fall out but I used duct tape in the top corners just in case) and re-installed the bead with the gap at the bottom center and then used black silicone sealant to cover the gap. Yes...silicone sealant. This is probably the only place I would use silicone on a RV. You can also purchase new beading from the link below if your bead has become brittle. Good Luck

http://www.pellandent.com/RV_Products_List.aspx?CategoryID=303