A Dehumidifier is your best bet.
I understand you were trying to avoid using one, but that's the way to go.
I redid an old camper this Spring. It had some Mold issues.
It took me a while to get it taken care of. (It had a leaky roof)
After I got it waterproof, I went around the windows and fixed a couple of poor fits.
I added rubber around the door to help keep out the cold/water too.
Working on my storage compartments was a little bit of work too...
I worked on that old camper Feb till May. Finally fixed most things on my list.
By far, the Mold was the most annoying to work on. Nasty stuff.
Work on yours a little at a time, get it right, then go camping...
I said that like it was easy... NOT EASY.
