That would be my first guess.
In the "dehumidifying" version, why wouldn't they use the local desiccating agent that they used for mummifying? I want to say calcium carbonate.
I know that we use calcium carbonate to melt road ice around here. Very corrosive on metal. Not certain what it would do to cloth.
I have to plead ignorance as to what they used for embalming. I thought it was some concoction of gum or myrhh that was placed in the body cavity to suck out the mosture. Perhaps salt has some religious significance. Perhaps none at all. We can have fun and speculate tho.