Are those really aluminum frames, Per? While I have only seen them on web sites - with the exception of the Tab - what I'm seeing is generally stamped steel. Since they are sometimes galvanized, not painted, they look like unfinished aluminum. Al-Ko
says "The AL-KO chassis is Hot Dipped Galvanised." I don't see a material indication in the BPW
information, but they looked like stamped galvanized steel to me, too.
I agree that these European designs are more highly optimized; they are also produced by chassis manufacturers (such as Al-Ko and BPW) which amortized development and tooling costs among many clients sharing a common modular design, while North American trailer makers tend to "brew their own".