After a lot of trial and error, I've come up with an efficient process for removing the heavy oxidation and corrosion from the window frames and creating a near-mirror finish. My method isn't cheap. It requires an investment in consumable abrasives, pads and polishing compounds. I haven't added it up, but I know I've spent more than $200 in consumables just to polish the 9 windows' frames. That's in addition to an air compressor and an angle grinder. After trying it a few different ways, I'm convinced the best tool for the job is a pneumatic 1/4" right angle die grinder. Get a cheap one for under $30 on eBay.
Here are the steps on the aluminum frames:
1. You can waste a lot of time trying to get the heavy oxidation off your windows with the wrong tools, abrasives and polishes. You have to overcome your fear and be aggressive. This isn't the trailer's ALCLAD skin so you can use tools you'd never dream of using on the rest of the trailer.
Use 80 grit (yellow) 3M Bristle Discs in the 2" size on your grinder. Grind all surfaces that will be visible after installation. Bristle Discs are going to scratch the hell out of your frames. But they're fast and they get all the oxidation and corrosion off that you're going to get off. You might want to buy a few 1" bristle discs, too, for tight spots. Do NOT use the 3M radial bristle discs. They gouge.
2. After you've scratched all the severe oxidation and corrosion off, you need to fix the scratches. Get some 320 grit and 400 grit wet sandpapers and hand sand everything you just took the grinder to. You have to go over it a lot to get out all the swirls from the bristle discs. Don't hurry this step. Clean frequently. Make sure the swirls are gone. Now instead of swirls, you will be left with finer scratches going the length of the frames. The second photo below shows the "before and after" of the hand sanding.
3. From here on, you'll be back to the power tools. Place a cotton 1.5" cylindrical or goblet-shaped buff in your grinder. Use Nuvite F9 polish and slowly polish everything that has been sanded.
4. Use a different buff to do it again with Nuvite C polish.
5. At this point it looks pretty good. If you would like, do it again with Nuvite S and a third buff, but I'd recommend waiting until it is installed back in the trailer before worrying about Grade S.
A note about what to polish and what not to polish... While you want to get all the oxidation and corrosion off all the parts, some parts of the frame don't need to be polished through all 5 steps above. Obviously the exterior of the front frame should be a mirror. But the backs of the back frames will basically not show at all and can be left in a clean but unpolished state.