The seal between the side and the tub is rectangular with a fin on one of the short sides.
The side with the fin faces to the top.
The open end of the fin faces inwards on the vehicle.
The fin fits into a channel on the underside of the side panel.
The long side of the seal on the outside of the seal is glued to the inside of the outside of the vehicle.
(hard to describe, easier to understand if you have one in front of you!).
Hope this helps!