I guess, you're all waterboxers...

The air channels, coming from the front air inlet, are
going through the door, where the first fresh/cold air
vent is placed. Then the ductwork goes up to the overhead
frame rails. In the Bus option of the T3 you got fresh
air vents left and right at the overhead frame rails.
At least this ductwork turns down to the engine compartment.
There it is attached to the alternator fan which pushes
the cold air through the heat exchangers at the exhaust
system. The hot air goes through a paper duct below the
van to the front. There is a small outlet in front of
the middle rear seat. The paper duct goes up where the
radiator is at the waterboxers.

Why are this channels taped? I guess, it's just rust
prevention for the upper frame rails. The fresh air
is not needed in the engine compartment.

Helmut
'80 Camper