I have tried to familiarise modellers with how common ferry vehicles were. These vans were the only large batch of ferry vehicles operated by BR, they provided the ships etc. and also a large variety of specially constructed wagons which were approved for continental use. A 4mm scale drawing of the van was reproduced as part of Bartlett, Paul W. & Mann, T., (1984) Cross-Channel Ferry Wagons used on BR in Model Railway Constructor Annual 1985 pp 18 - 29, edited by Leigh, Chris.
International Ferry wagons European and British
Because they were air braked the various BR ferry wagon designs were useful for conversions, so despite small numbers they tended to survive for a long time.
It does look like an impressive model. I must admit I am grateful it is too late for my modelling period, rolling the roof would be the least of my concerns when looking at the underframe!
Paul Bartlett