The desert sounds like the best approach.
I don't regularly treat anything.
There are a couple of aspects of black Cavendish that encourage a mold problem. The first is our experience with commercial Cavendish tobacco. It just seems like it can be left slightly squishy. As a result, it's tempting to not dry it sufficiently for storage. The second is that the Cavendish (cooking) process damages cell wall integrity, increasing the hygroscopic character of the lamina, and as a result, it will more easily draw and hold onto moisture from humid days.
If you don't own a desert, Cavendish can be dried to a state that is barely flexible (low case), but then enclosed in a vapor-proof container so that it will not backslide by absorbing moisture again.
The only, only, only tobacco that I've had mold as a batch in a bag is some shredded, homemade black Cavendish--and only once.
If you pressure cook it in a Mason jar, and never break the seal on your lid, then it's not going to mold, no matter how damp it is. Once you peek, you've got to dry it down or resort to chemical anti-fungals.
One might wonder if Perique, with its damaged cell walls, has a similar predilection to molding. It doesn't seem to. I believe this is because of its more alkaline pH, and the high osmolarity of the goop that leaked out of the lamina. But I now shred and dry it to low case, as soon as it comes out of the press, and store it in a vapor-proof pouch. (I used to store it as a wet slab in double Ziplock bags inside the fridge. Wet Perique stores that way for years, with only scant signs of yeast growth.)
Bob