Has anybody retro fitted a central locking button to their Mercedes based Carthago? Lockers and doors can only be locked or unlocked using the key fob, or unlocked by opening the passenger door. This is really inconvenient because the alarm is set each time. The doors are locked automatically after driving off so when stopping and getting out of the habitation door the lockers are still locked so I either have to take the key fob or open the passenger door first.