Unless it changed this year, the JayFlight fiberglass option is still hung over wood framing it's not aluminum framed.
I did call Jayco a couple years ago when we were shopping and the fiberglass option added 500-600 lbs I recall on a 29QBH.
After seeing the JayFlight fiberglass siding in person I decided against it. It was Gel Coat or high gloss, to me it just didn't look as good.
2007 Chevy Duramax LMM/Allison
2012 Jay Flight 29QBH
2012 Jay Flight 26BH (Sold)