The Class 489s were converted in 1984 from ex Class 414 2-HAP driving motor cars, into driving luggage vans to operate on the Gatwick Express. These acted as driving van trailers on the London end of the Gatwick express and usually operated with a rake of specially converted MK2F coaches and Class 73s. The last 489s were withdrawn from service in 2005 when they were replaced by Class 460s.
Network Rail bought three Class 489s for use as load bank and deicing vehicles, in 2010 Network Rail refurbished their 489s as well as adding a number of modifications including additional headlights, removal of the headcode box and removing most of the bodyside doors except for a central roller shutter door. It's in this post refurb condition that this model is depicted in. They can be seen quite commonly paired with a GBRF Class 73 on most parts of the Southern Region.
This model uses certain elements of Wessex Electric Nutters MK1 Suburban coach, PCV parts and EPB textures. So credit to him for some of the mesh bits.