That may be true. I know that in the 1967
Overlander, there is a hole the goes through the floor right on top of the black tank. The same duct also exits under the tub to heat the bathroom. I will dig through my photos to find a shot that shows what I'm taking about. It may take a little while as it is getting near my bed time.
Found them, I hope I do not get in trouble for posting these. I was given a collection of photos from a friend from the forum to use as reference for my project.
One shows the duct removed, the other the floor with the hole that goes down to the black tank. The last one I hope you can see the duct inplace with the hole. Again, this is in 1967
, so yours may be different.