Tannus inserts can help prevent flats, but when they don't, they are more work than just tubeless to replace. My advice is, if you are concerned about getting flats on this trip, just replace the tires and sealant with high quality tires and sealant before the trip.
Another thing, for trips like this, don't change anything at the last minute. Have the work done, and go for a few rides first before leaving.
You are overthinking this. The Rohloff and Gates belt are the Cummins diesel of drivetrains. As long as your bike has been maintained well, you have nothing to worry about.