Traxless; as you've undoubtedly already discovered, it's hard pulling information out of the Outdoor RV website. There are three separate layers of insulation in the roof, starting with, apparently R15 Astro Foil, then two layers of fiberglass. It would appear that the roof has substantial insulation. Their material is silent on what the roof is constructed off, so I'm guessing wood trusses, and I think the roof is rubber.
Yes, the wall frames are "bonded" aluminum, which might mean a combination of welding and bolting. They apparently have wood inserts in strategic positions for screwing cabinets, for extra strength. Between the aluminum framing is styrofoam, and you can see the nature of it in the interior seats. They use the outcuts for doors and windows as the seat bases in the dining room. In discussions with the Canadian rep in Alberta, he tells me the window and doors spaces are cut out by computer guided machines, and this means a precise fit for the frames,which is a good thing. Nice, tight, tolerances.
Mine is the 19B, but you'll have to wait for the end of next season for reliability updates. In puttering around the trailer now in storage for the winter, I continue to be impressed with the construction, and it definitely tows better than my previous trailer, a lighter Pioneer Fleetwood of similar size, and the electric brakes are definitely better.
Will be happy to post further reports at the end of next season....
Hope this helps, although not much in the way of definite confirmations. Maybe other owners who have toured the factory can kick in some comments?