>  1)         Where does the exhaust air go from the vents on the lower
>  back corner of the front doors in a 1983 V'gon? The vents simply open
>  into the cavity of the doors behind the fibre board panel. No outlet.

The Wolfsburg engineers found that the dense air deflecting around the
flat front and back along the doors of the T3 created a substantial
vacuum right up front, exactly where the front edge of the door seam
is. Being altogether clever by half, as VW engineers are (were?), they
decided to utilize this vacuum effect to ventilate the vehicle. Cabin
air is sucked in through those vents at the back of the door, through
the door cavity, and out the front edge. This worked adequately, but
was supposedly noisy and really only ventilated the forward cabin
area. 88 and later T3's have "flow through" ventilation via exhaust
ducts in the rear windows just forward of the D pillars. An additional
rubber seal in the front door edge blocks the whistling vacuum egress
and the rear "door vents" are blocked up, being only hole fillers. I
am not certain where the air actually exited the door cavity in the
early vent design. My '90 does have a painted-over sticker on the
door, tucked back outside the door seal at the forward edge, up by the
upper hinge that appears to be covering a hole into the door cavity.
Perhaps that's where the air was formerly exhausted?

>  2)         Do the holes along the bottom of the rear hatch serve any
>  venting or draining purpose? Or can I fill them with Great Stuff as part
>  of my noise insulation project?

That row of slot-shaped holes along the bottom, right? I think they're
open to the interior cavity of the hatch. I'd be wary of filling them
with stuff. I've never had a leak into the rear hatch cavity, but if I
ever did, I'd want free flowing air to be able to dry it out! Besides,
you'd probably get better soundproofing results by pulling off the
hatch panel and applying soundproofing material directly.

--
John Bange
'90 Vanagon - "Geldsauger"