Many (most ?) new travel trailers are now using aluminum square/rectangular tubing the structure in walls. Some type of rigid foam is placed in the cavities. Internal and external sheathing is typically luan plywood (inexpensive and lightweight) or some type of non-organic panel (Azdel). The outer "skin" is typically a continuous roll of another non-organic (Filon).
I know in traditional "stick framed" residences, the sheathing is used to prevent the wall from racking along the face of the wall. It also provides a surface for attaching the finished exterior "skin" (vinyl, cementitious, etc siding) . Before plywood was cheap and plentiful, 1x6 material was diagonally "let in" to the 2x4s at the corners to prevent this racking.
The rigid foam insulation used in a TT is obviously not sufficient to prevent the wall from racking.
If other means were used to prevent the walls from racking, could the rolled non-organic material (Filon) be applied directly to the studs and rigid foam or woul the "print though" ?