In the 70's trailers, the window hangs from a hinge that will release if you lift it up high enough (ie., well past horizontal). If you want to remove the glass from the frame, it depends on the window. For example the front center window and back center window will come out of the frames by first drilling out the rivets that hold the hinge to the top of the frame, then there are two rivets at the top center, and two at the bottom center that if drilled out, will allow the frame to separate into a right and left half, and the glass to slide out from in between.
Finding the rubber gasket that fits perfectly around the glass and into the frame is a challenge. Not being able to find what I was looking for, I ended up sealing mine back up with a generous amount of vulkem and calling it good. The stack or vista-view windows are completely different, as they don't open--there are several threads on the forums regarding their rebuild. The front wing windows are also have a unique set of challenges.
I rebuilt my front and back windows because they were made of some kind of acrylic and were cracked. Also did the vista views to deal with the double panes and the peeling tint. Recently did one of the wing windows to rebuild as a single pane (the other is on my list as well). The other windows, I simply trimmed the edge of the dried out rubber gasket away and ran a bead of vulkem into the junction of glass and frame. Sealed them up just fine.