i am from canada and my 1970 camper was origionally sold here with a "cold weather package" nothing major other than a gas heater and an external oil heater that bolts on to the bottom six bolts on the oil screen. as for ductwork i think they were standard two under the back pull out bed/bench ,one in the centre in the floor between the two front seats and regular defrost and floor settings. nothing in the door though. i also have a propane furnace but i think it is an after market as not the origional,it had long since been replaced for some reason.
If there were vents in the door of this other bus than im wondering if this was a transporter then later changed to a camper to fit the owners needs.
I hope this answers your questios.
good luck
64 sunroof beetle
70 westy camper (sheila)