I talked to Nuvite and they said that Nuvite S has protectant in it and they did not recommend any sealant.

Unfortunately, I know of no substance that will seal polished aluminum.  A trailer that is outside will likely need some polishing at least once a year.  My best advise is to keep your polished trailer clean, dry and covered with soft cloth.   I find glass wax to be a wonderful substance to clean with and I think it also provides some short term protection.  Below are pictures of our latest protective efforts - complete with a rope and pulley lifting system . . .

Sealing polished aluminum and having it retain its brilliance has been the pursuit of many, but it has yet to be achieved.  When you find the solution I am sure the folks at Airstream will be very interested ;>). 

It is important to clean the outside of the trailer after a trip.  The dirt and grime just gives oxidation a great starting place. . . 

Cleaning - Water wash with no soap - DRY so it is completely dry with the microfiber cloth! I usually spray a little glasswax on as I am drying.  This helps make sure I remove all the water and don't leave any water to spot.  The video suggests The Absorber - I have not tried that product. 

Microfiber Cloth

This is great for drying, dusting and cleaning off water spots. So far I have only used the cheap ones you can buy at Costco or Walmart. You can purchase better ones and they might be worth it (see http://www.properautocare.com/micwhatbigde.html).  I dust with a microfiber cloth (either dry or just misted damp) to remove any dust. Then, if there are water spots, I mist on a small amount of glasswax and dry that off with a clean microfiber cloth - water spots are gone and the trailer is shiny.  If it is really dusty, I dust with a California Duster (those red mop looking things) first.

Well, here is our "ghost" trailer - just in time for Halloween.  We have put it in the hanger back behind the airplane for the winter to keep it out of the rain.  Since it is out of the wind and the elements we covered it with sheets to keep the dust off.  We made a pulley system so it is easy to remove this dust cover.  We have a fan that we leave running in the hanger to keep the air circulating to reduce condensation.  We will see how the polish lasts.  On the bottom  is our Luscombe Silvaire - Waiting for its polish job!