My old Transit was fine, i had carpet on the floor, dont know if that soaked up the moisture. I used to leave it open every morning for half an hour when loading up etc.
I had to scrape ice off inside of windscreen this morning as fan heater wouldn't shift it, does that mean air filter needs changing? (I's a tiler, not a mechanic)
Cat litter, it was cheap and siaks up the moisture.. or saw dust if you can get any.. i used to fill old socks and put them inside the van. Or just put it into open boxes/ cat litter trays if you have the space.. right mess if you knock it over though..