Try one of those little chemical dehumidifier things. I have one with the
trade name of "Dri-Z-Air" (groan) and its just a basket containing Calcium
chloride (granular and replaceable) over a little pot/tub. The CaCl2 sucks
the moisture right outta the air and the saturated CaCl2 solution drips
into the little pot below.

It works well in reducing the condensation in my van, but I am not living
in my van, you may be replacing the CaCl2 quite often.

Alistair