What's with the ridgey exterior walls on the Jayco TTs?

Aluminum is definitely "greener" than any/all composites. In addition to the obvious simplicity-of-manufacture (which doesn't involve the kind of chemical stews required for composites), it's one of the very few materials in the RV-making world that are truly and continuously recyclable.

The siding on that new trailer may well have been aluminum window frames in a former life and it'll be reused again once the trailer goes to the wrecker...not so with composites.