In this picture a portion of a Met-Camm vehicle has been created, and will likely have been to try out the styling of the seat with the paneling.

While the design panel had influence in all DMU designs, this was normally limited to items such as colour co-ordination of interiors. But by the time the Trans-Pennine units were built they had much more control, and an external industrial design consultant was used. This mock-up served not just to try the cab layout, but also to pick the best location for the four-digit route indicator on the outside, with it being tried on the front of the roof dome. 

As well as for design use, mock ups were built for promotional use. A Derby Lightweight cab has been seen on the back of a lorry during a fair in Derby, and a Blue Pullman cab in Repton college for an open day. This wooden mock-up, numbered 51401 contained a cinema which seated 62, an information bureau and "sectioned scale models which operated at the touch of a button". It was built for the "Boys' and Girls' Exhibition" held at Olympia in the early '60s.