K. Nok,
They giving the suggest that they are using and not any problems when exterior use so exterior grade plywood with wooden frames, the skid, floor, header would be as per the drawing the frame and cross bracing suggested in the spec are 1" x 4" but we can reduce the 1" (25mm) to 0.75" (18mm). The sides and roof would be 3/8" exterior grade plywood rather than lumber (5/8" x 6") which would be cost saving for us.
Anyway, if the sample meet the dimension as above so should be not the problem.