I used to live in Gravesend (pre-scooby days) and really don't know that theres anywhere 'decent and secure' - the carparks are all very much typical carparks I'm afraid. Depending what sort of time you're looking at you might get parked in West Crescent Road just behind Harmer St on the one way system behind Chalmers motor spares shop - Jim , Dave and Jason might then be able to keep an eye on it for you. Might pay to have a word with them first - get back to me if you want. The only other suggestion is to speak to Pele as she still lives in Gravesend.