Jayco Aluminum structure

I know that Jayco stopped making the all aluminum structure in 2003 or 2004. I'm interested in buying an older Jayco 5th wheel and much prefer the all aluminum structure. Does anybody know which models/years they made the all aluminum structure? When I say "Aluminum structure", I'm referring to all six sides with aluminum studs 16" on center. Is there something in the model number that would indicate the aluminum structure? Did all Jayco models have it? I have searched all available sites I can think of and can't find any information.