I would suggest you need a small consumer unit with three circuits, the unit should have a master RCD and each circuit should have its own RCD. Probably 15 amps for socket and heater circuits and five amps for lighting. Generally on campsites you are unlikely to get a supply greater than 16amps in total! So a 20 amp RCD as a master should be adequate. If it is a fixed heater you could have a smaller RCD, 1kw is about 4.5 amps. I would question why you want lighting as I would assume if you are on hookup you will, ideally, have a charger set to automatically charge your vehicle and leisure batteries in which case use the habitation lights, one less mains circuit to mess about with!
if you search on the web for RCD wiring diagram you will find any number.