The Siesta end gap is a giant air scoop

[Swift]

The 8” wide piece of trim that covers the gap between the rear wall and ceiling of my Sprinter 24SS became detached several times. While attempting to secure it again, I discovered the adjacent wall and ceiling to be soiled with a film of black road grime. A peek under the rear of the unit confirmed my suspicion that the bottom of the fiberglass rear cap was acting as a wind scoop. When driving at highway speeds, the area within the cap becomes pressurized, causing the trim panel to blow loose. My fix was to stuff the cap’s entire upper cavity with household fiberglass insulation and reinstall the trim panel with #6 screws. (I don’t own a pneumatic pin nailer.) I haven’t driven her yet but am confident I have resolved this annoying issue.

[paulwadley]

What year and model Siesta do you have? I have a 2018 Siesta 24SS and have not noticed that issue but I will be taking a closer look at mine to see if I have the same issue.

[Swift]

It's a 2018, just like yours.