If it is to clean the cigarette lighter socket (and many other things besides, electrical and otherwise) get a fibreglass cleaning brush, such as item B003YSWJDG from Amazon UK.
Search Hella Kleenaplug on E=Bay and it comes up, just got one. It is to 12s/12n sockets what the battery terminal post and clamp brush is, if you know what I mean.
A simple solution would be to install a socket insert into the stowage location on the A frame for the caravan plug.This would ensure plug pins are cleaned each time the plug is inserted/withdrawn.