How to the door caps that cover the weatherstrip (door/window seals) remove? Specifically the rear doors? There is a popper at the bottom but I can't tell whether that's the only one and it should now slide off or if there are others (and where they are).

Opposedforces and the User Manuals detail the screwed frame and rubber seal as the "Weatherstrip" but both seem very vague about the cover/caps.

This shows the Retainer Moulding assembly and the rubber weather strip:

http://opposedforces.com/parts/impre...llustration_1/

What I need to know is presumably the "Cover Assembly C-Pillar" - which I can't find any mention of anywhere.

 

A photo of what you are actually refering to would be helpful in this case
I think what you are refering to is all part of the weather strip retainer/moulding assembly (items 2&3 in the diagram)

The actual rubber seal just pushes into the retainer with a push clip at the ends.

As this forester side visor document illustrates
forester side visors pdf

 

 

As per my previous reply - all part of the weather strip retainer/moulding assembly

Pull out and remove the rubber seal and you will find all the screws as per the opposedforces diagram.