Ok lets get up to date, shall we?
I was getting a little frustrated with the selection of RV windows I had available, as I only had one single-pane window, and needed 3, one for each bunk, and one over the sink (since a double pane one would wind up behind the countertop's backsplash.)
My dear friend, Stretch, suggested something that sounded absurd... perfectly ludicrous! Since I had several extra double pane windows, he said "Why not just cut them down?" Why not indeed!
Windows in its original form is on the right. Resulting window beside it.
I had to remove the screws holding the top of the frame to the sides.
Removed the top of the frame.
I then marked the side frames for cutting. I measured from the rivet holding the top window pane to the top of the frame, marked the same distance up from the bottom window's rivet (rivets are on the "exterior" side of the window's frame - depth wise). I then measured from this mark to the top edge of the frame, and marked the same distance on the "interior" side, and created a diagonal line that matches the angle of the top of the side frames.
Drilled out the rivets holding the top window in, and since it was still attached to the arms that actuate the window, rotated the window out of the way for cutting.
I used a cutoff wheel to cut the side rails. I cut right through the actuating bar for the top window while I was at it.
Reattached the top frame using the same screws I took out and Viola! A single pane window!