In essence, it's very much like an urban adventure. The same number of NPCs as a small town. Social encounters are done around a campfire at night, rather than a tavern. There would be a number of different 'taverns', since most caravans are made up of a number of different merchants who have signed on for the trip - safety in numbers. Town guards=caravan guards. As for adventure opportunities, you can still have mysterious murders (Orient Express), thefts, attacks (read: typical first level goblin raid on village). You can have side adventures if the caravan is stopped by a blocked pass for example. The flavour text changes, but the kinds of things you can do with it is very open. You could even do political/war themed stuff if the caravan finds itself penetrating ever more deeply into a war zone. (For those who have read A Song of Ice and Fire, think of the Yoren/Arya's trip into the war zone of the Riverlands. Each day got a little more frightening and surreal. Everyone else was going the other way.