The steel framed/alum.skin trailers were called Valuelites from late 97 until sometime in 2003, when all of Sundowner horse trailer models were named Sunlite with a model number following the word SUNLITE.  ALL steel framed trailers went out of Sundowners lineup in Dec. of 2007.  All Sundowner models have been aluminum framed since Jan. 2008. 

 The Sunlite models that were steel framed were 707, 727, 728, 737, 777, 777SR, Stampede's, 747, or 767.  In other words, any model number that ends in a "7" was a steel framed trailer from 2003 thru 2007.

I might ad that, the main source of problems resulted in trailers in the midwest and northeast; in which trailers used in winter months with salt and chloride used on roads in this part of the country resulted in accelerated deterioration of the steel frames.  However, the majority of these trailers haven't been affected, and are still giving excellent service for their owners.

In the earlier post; the VIN number is a very simple way to tell; ALUMINUM is LA or AA followed by four numbers (last six of the VIN); and the STEEL framed models will be VA, VB, VC, VE, or HA and ZA in the case of steel framed living quarters.  Hope this clears up the confusion.

Please be aware that this is an opinion from Jim Bob. Trailer repair shops located in other parts of the country that do not have salt are reporting the same types of issues. You should look carefully at each and every unit you are considering.

If I understand correctly, a 1997 Sundowner Sunlite Aztec would be steel frame, aluminum skin?

Kim