I don't have that problem. The things I do are: Not to have it cocked so there's no salt in the chamber and I lay it on its side under my coffee table away from sunlight. Laying it on the side prevents it from entering the hole. I use Aldi's table salt and I don't know if it's different from the Coles table salt. I wouldn't put anything else in there. I hope that helps.

Edit: Maybe try decanting some salt in a jar and throw some silica packets in there and only use that for your gun.

https://www.wikihow.com/Prevent-Salt-from-Absorbing-Moisture

I was going to suggest trying salt with an anticaking additive but the Coles iodised salts already seem to have it.

Haven’t seen the guns in person… Is the salt reservoir large enough to accommodate a tiny silica packet like the kind found in vitamin bottles? And would it interfere with firing?

You could mix in a small amount of bicarb to try and help keep it dry and free flowing /shrug

Edit: Found this. 3:53 onwards talks about humidity and salt clogs but it doesn’t address your particular problem https://m.youtube.com/watch?v=NsFzz5kjFpU