It actually seemed to work well; the Southern had long had the knack of handling portion emu services, something which seems lost nowadays. When Gatwick opened up the special shuttle used the eight post-war 2-HAL units, which looked like a 4-SUB, and which had been built as replacement for pre-war electric cars destroyed in the war. They started the approach to be attached to the front of the 2-BIL Arun Valley services at Gatwick, and on the return be detached from the back. One of the through platforms at Gatwick had 2-way signalling (unusual then), crossovers, and a shunter on duty to handle the couplings. When these changed over to 4-VEP units, Gatwick had built up quite a bit and a separate normal 4-VEP was used, later modified to the VEG units with luggage space etc, but still 3+2 seating and doors to each bay.
British United Airways, the 1960s principal airline at Gatwick, used to have a check-in upstairs alongside where the Gatwick unit pulled up at the buffers, where you could check in and leave heavy luggage, a porter brought this down a few minutes before departure and wheeled the trolley into the guards van, which was then taken at Gatwick directly to the airline baggage facility.