OK, well. . . couldn't get the pictures to post, so here's the description. See my photo list for the pictures.
After you get the retaining ring out, use a small flat blade screwdriver to pop out the plexiglass inner pane. I didn't reinstall mine, so I just cleaned it and saved it for posterity.
Once the inner pane is out, get a helper to push on the outer pane from the outside of the trailer toward the inside. It will probably pop loose easily. If it doesn't, don't rush it! They are expensive! Once you have the pane loose, then pull it out (from the inside of the trailer). It may take a little persuasion to get past the plastic trim, but it will come out.
Take the outer pane to your workbench and clean it thoroughly. There is a mylar fim on the glass that may or may not be immediately apparent. Use a SHARP razor blade scraper to CAREFULLY remove the film. Once you have it off, clean the glass thoroughly. I used Barkeepers friend and a "white" scotchbrite scrubber (like you use on bathroom tile) to scrub the glass clean. The Barkeepers Friend doesn't scratch when used with the white pad.
Go back to the trailer and clean the frame for the window using laquer thinner or mineral spirits (same thing). Acetone evaporates too quickly to be of much use.
Once everything is spic and span, place a generous bead of Vulkem on the inside of the frame where the glass sits. pop in the glass.
IMPORTANT!! You will need some type of gasket to hold the glass against the frame of the trailer. I have been told that Vulkem will hold it by itself, but I used a 1/2" by 1/2" closed cell foam gasket with adhesive on one side and a urethane facing on the opposite side to add some insurance.
Apply the gasket with the adhesive toward the frame (90 degrees to the glass) so that the urethane facing will be visible once you have it all back together. (see pics)
Once the gasket is in place, reinstall the aluminum retaining ring (which will push the gasket against the glass and create a compression fit). Go to the outside of the trailer and wipe off the excess Vulkem. Be careful not to wipe away too much. It will shrink somewhat as it dries.
You want to leave a smooth bead to shed water over the outside frame of the window.
Add some new Vista View trim (available from Inland and others), crack open a cold one, and enjoy your "new", clear, and water tight windows!!