[Mikendebbie]

In the youtube video "Keystone Montana factory tour" from April 2019 - at the 31:13 mark - the Keystone guy shows the current wood trussed roof and says they changed back to wood trusses to get better connection of the wood roof deck to the trusses. He says that in the past they have used aluminum trusses, then stamped steel, then carbon fiber, and now they have gone back to wood.

I looked back thru some of the archived brochures on the Montana website and this is what I found...
2001 - 2004 - 5" welded aluminum trusses
2005 - 2012 - fabricated galvanized steel trusses
2013 - 2018 - brochure refers to them at "arched rafters". In a youtube factory tour video from 2011, the trusses look like aluminum. The pic below is a screen shot from the 2011 tour video. There might be some disconnect between the brochure info and the pic below...beats me.
2019 - 2020 - wood trusses...I suspect the flat ceilings that came in with the 2019 models were partially a result of incorporating the wood trusses.

I only looked at "Montana" archived brochures...not High Country or Big Sky etc. etc. Those brochures may state a different roof construction.