i had some recent success with rock salt. A very nice chap from here
@Pmal027 suggested rock salt in bowls to absorb humidity from the air. It was nice and cheap and did bring RH down. A few bowls of rock salt around the space. I then tried a couple of my wifes Himalayan Salt lamps. The kind you put tealight candles in. I put 3 medium sized ones in my tent (on saucers) and it did the same job as the bowls of rock salt. The difference was i could bring the lamps in in the evening and put candles in them and they dried out and were good to go again the next morning.. 😵