Allen, I think the sealing with beeswax at the seams is good ( to seal against moisture), but I don't think any other coating is necessary on the inside. I have read all I could find on forums about salt/rum/spice horns and haven't heard anyone talk of a need to add anything for any spice,only liquids.
I have only built two, and no complaints so far.
hopefully someone with more under there belt will chime in soon.
Nice horn by the way