The sliding window in a Westie has the catch in the center of the window while
the sliding window in a non-camper usually has the catch near the window
frame.  I say usually because I don't want Chris Turner flaming me about
certain non-camper models that have the catch in the center (like some early
non-camper, non-pop top Wolfsburgs I have seen).  The reason for the
difference is that the camper window has to allow for the screen while the
normal non-camper doesn't have a screen.
Hope this helps you,
Ken Wilford
Van-Again
John 3:16