The word was the Mr. Heater, and others, catalytic propane, create a lot of
water vapour in a Vanagon.  That seems to be fake news, or perhaps an
exaggeration.
   I've been running two now, in the wet southwest desert, one in a camp
trailer and one in the "annex" (my Vanagon)   Fairly humid here now,and no
interior moisture problem at all.  Perhaps the catalytic combustion is
dryer than people have said..
    Now when I ignite the Westie cook top, the Vanagon steams right up,
immediately.
     So there you go, a report of one family's (two humans and three large
Chesepeake dogs, full timing with two Mr. Heaters as our comfort heat)