I have a 2008 25fb Classic. I had a water leak coming from the plastic flashing around the hinge side of the shower door. Its easy to remove the shower door frame and flashing to caulk.
I'm going out to my Airstream today after work. I'll check my shower door tonight to see what your talking about. Maybe you can post a photo too. If I remember correctly the metal threshold should channel water back into the show pan.
2008 Classic 25fb "Silver Mistress"
2015 Ram 2500 6.7L Cummins. Crew Cab, 4x4, Silver