Currently the easiest/cheapest way to gather rare permanent upgrades is to install an alt, harvest the rare ressource (e.g. Cartagena Tar), craft the module and put it in Captains Chest for easy transport. But why on hell a sane captain would stuff his personal travel chest with Tar? Or Copper plates in case of Copper plating if we get copper city? On the other hand books were in the age of sail a common content of captains chest and mostly small and lightweight enough for the chest.
Therefore i suggest to swap these two types of items, let the personal skillbooks be stored in captains chest (and transported by tp), and the permanent modules only transported by ship. So we additionally get some reason for smugglers and traderhunters to linger around ports like Cartagena or Coppercity together with great opportunities for pvp :-)