If it is like most out there, it will be somewhat dirty inside and out and may need some repairs.
First step is a good cleaning.
I use TSP trisodium phosphate cleaner. This is found in the paint department of most big box or hardware stores. It is relatively cheap, strong and one box will clean most trailers.
Mix the chemical with water, according to directions, at the strength you think you need. Remember to wear rubber or neoprene gloves! Thi stuff is strong and harmful to skin.
Also wear googles or other eye protection. Hose down the trailer and then brush on the TSP form the top down.
Here is where you appreciate a good solid ladder. I prefer the platform type, or a scaffold.
Begin on the roof with a long broom or handled brush. An extendable RV cleaning brush is handy and will last you for years.
Wash the trailer and then simply hose it off. This is a good time to check for interior leaks, especially around the vents. Check in cabinets and closets also to see if there is water getting in.
If you find any leaks, you should make note of what is above the leak on the outside. A vent or cap is likely to leak around the seams. But leaks also travel. You may find a space in a seam where two panels meet and the leak will come out on the inside quite a ways from this spot.
Seam sealing is the only way to prevent this, and remember there may be leaks inside the wall of the trailer. The Airstream and other brands have an inside wall covering an inch or so of space between the outside wall, and usually filled with insulation. The floor can tell you if there is an inside wall leak, look for water stains by the wall where it may be soaking on the inside.
A serious leak can require removal of the inside wall and then attention to the frame beneath.
This is another topic of itself. Removal of plywood subfloor and replacement can be a major job, but not always necessary.
A small area of wood damage or rot, can be cut out back to solid wood and a piece "scabbed" in to fill the space. The repaired area should be well sealed and a wood putty or fiberglass/ epoxy mis can be used, When sealed this will be as strong as the original floor and will be water resistant.
Marine grade plywood can be used but be aware of chemically treated wood used in an indoor space, which may off gas harmful fumes.
Back to the outside: If you are going to polish the trailer, assess the clear coat if any. Try a small amount of metal polish on the surface. If it turns the rag black there is no clear coat present.
The coating may be gone in one area or all over, it is wise to check a few spots.Sun damage can and will break the clear coat down and it may be obvious where this has happened with rough edged dull spots visible.
To remove the clear coat, you use an Aircraft aluminum stripper. You can get this at any auto parts supply or hardware type store. One excellent brand is RemovAll . This is environmentally friendly stuff that you can hose off into the grass or driveway with no ill effects. Try some on a small area like 3 feet square, near the bottom of your trailer. Let is stay on as the instructions say, then hose off. A pressure washer is handy for this.
The clear coat will literally fall off, and should be hosed off the driveway and trailer completely. Any remaining coat or chemical on the trailer will dry in the sun and be harder to get off later. Trust me on this!
Once the clear coat is gone you may find that your trailer looks shiny enough for you, and with application of a good auto wax or sealer it will be done. For those looking for the ultimate mirror shine that older trailers ( pre-brushed look) can attain, there are many sources for how to do this level of polish. One goo source is JESTCO products who sell materials and instruct in proper polishing methods. Be warned- a highly shine trailer will require regular maintenance to keep it that way. One stored outside will become a regular chore to stay at that level of shine. This is where your personal tastes come into play.
Even a non stripped but clean trailer will look great. A shiny 20 footer ( meaning the view from standing 20 feet away) may be just your desire, and is my personal one. But others want a competitive super mirror shiny level, and will not stop until they get it.This is totally up to you.
Your first job is to get the trailer leak proof, clean and ready to enjoy. The shine up can wait.
This level of shine takes a lot of work and regular care. But it does look great.
There is nothing wrong with a clean non-stripped trailer either.
