Kallos's journal(s) is with him IC, a book at the bottom of a chest half full of other writing and magical implements. It's binding is leather, the parchment within is what one would expect of any common book, and written within are the research notes and personal thoughts Kallos thought were important enough to write down. While it could be stolen or lost, it isn't useful to anyone that can't read Isurian runes. Some pages may contain glyphs of the... damaging nature.
Letters will be kept separately, if anyone ever sends him one.(but still, posted here)