You'd need to be going the same direction, roughly same distance, at the same time, and you need to be ready to sail when the wind is right. I don't know when I'm going to do my hauling - the time has to be right, both in game and IRL. People in warships are generally doing something with them, somewhere else. They aren't going to zoom up from a region or two over in time to help you.
Also, even clans have spies, and advertising your trading outposts even among friends will dry them up.