A last point on all assigning your own troops to a caravan by finding them on the overland map and asking to inspect their troops. You can make make a Carvan much more resilient by assigning high tier troops, however, this will cut heavily into the caravan's profit margin though. All cavalry caravans will be much more survivable since they are able to avoid bandits and enemy armies, but that also means they will spend much more of their time running away from bandits than doing actual trading, which again cuts into your profits.