To begin, figure out what size screw is holding your windows on, and purchase new stainless steel ones. The screws used on my '63 Lo Liner windows were 8 x 3/4" long sheet metal screws with a 1/4" hex nut head . I bought a special drill or driver attachment that will fit around the screw head and they come out pretty easily, except when the screw head is really rusty. It seems to shrink a bit. So I grabbed a 1/4 open end wrench and removed them manually without the drill or driver. Remove all screws, making sure to keep your hand against the window when you remove the last several screws. You don't want your window to fall out.
I take a bucket of hot water and use Murphy's Oil Soap and a stiff cleaning brush, to scrub the aluminum and screens clean. Rinse with the hose with a strong jet of water. I then take a 3M or Scotchbrite cleaning pad (be careful not to scratch aluminum) and with the oil soap and water mixture, scrub all around the window aluminum. If there are some small spots or rust to get to, I use a fine brass brush, they are small, they are located in the paint department of your hardware store. I also use 0000 steel wool, which is very fine and won't scratch the metal, but the more abrasive Scotch Brite pads have the potential to scratch the aluminum. You can also use a metal polish, after doing the above steps. Sometimes the metal polish will brighten the metal more. If your aluminum is badly corroded and has a type of corrosion dust, I have seen a product for cleaning aluminum, located where you find Navel Jelly rust stripper at Home Depot. You can also get ambitious and use a Dremel rotary tool with a polishing head and some rouge polish. That's getting pretty ambitious for me...I want to get out and go camping.
Update! My hubby decided to do some extra polishing on the window frames and gutter rails. So he bought some polishing attachments for our drill, a can of polishing compound, and they turned out beautiful! Alot of work, but it sure is shiny. Not all of the corroded areas shined up, but some did.
If the screens are rusty, I usually clean them up really well and then spray paint them with Rust Oleum Aluminum colored paint. You have to make sure to scrub the Murphy's Oil Soap off before painting, because it is made from vegetable oil, and will prevent the paint from sticking well. So you may want to use ammonia and hot water on areas that you plan on painting. Ammonia is a great cleaner.
I then take a scraper and remove any of the old butyl tape around the back edges of the window, that goes against the body of the trailer. I scrape any remaining on the trailer and often use Goof Off to remove any glue or putty residue on the trailer. Take your roll of butyl putty and place it around all 4 sides of your window frame. You then butt the window up against the opening of the trailer and line up the screw holes. Put in new, STAINLESS STEEL screws, so that they won't rust over the years. I usually drive in the new screws every other hole, then fill in the remaining other screws. The putty will often be squeezed out the sides, so take a PLASTIC putty knife to cut away the remainder.
I noticed the back window on the Low Liner had a little leak along the bottom, so I bought some window CLEAR silicone sealant, and placed a thin bead of it along the glass and aluminum to keep water from leaking in. This worked wonders for my past Lil Loafer trailer, and thank goodness, cuz I camped out in the rain twice in 2011 and it was ALOT of rain.
I took some pics to help you understand my little process:
Use a wrench to remove a screw head that has rusted and the drill can't grab the head.
I order these from Ace Hardware.
Screws, drill attachment, wrench and driver.
Windows are waiting to be put back on.
Butyl putty or tape.
The 8 x 3/4 stainless screws I use.
Scotch Brite pads and 0000 steel wool
One metal polish product
Badly corroded aluminum.
Murphy's Oil Soap, Scotch Brite pad and elbow grease.
Here I'm placing the butyl tape
All cleaned up and ready to install.
