I recently realized that there is an easier way to transfer collected caches for offline usage:
There is now a new button “Add GCs to List” which adds all collected caches (e.g. those you’ve collected for a day trip from the map) to a bookmark list “XCTransfer” in your geocaching.com account. This bookmark list needs to exist with that name before you press the button, it also should be empty (unless you want to add additional caches).
Once your collected caches are added to that list, go to “My Bookmarks” and create a PocketQuery for this list. This PQ can then be downloaded as usual for offline usage.