Lee,

Well since I just got done (almost done anyways) with the R&R on my
1980 van I guess I can chime in here.
baseline, my 1980 ASI camper is a base model transporter, shipped to
ASI Riviera motors in WA state.
it had a non-fan 2 piece underdash heat/fresh distribution box..  VERY
DIFFERANT from a fan powered one I took from a 80/81 Westy.
lets hop you have the fan powered, not mine

anyways..  the stock aircooled box is the same as the box
w/heatercores. even has the knock out for water outlets..

make sure you have a LONG (very important) HANDLED #3 (again VERY
IMPORTANT) PHILLIPS with a good grabby grip.
and be sure to get ALL of the screws out.. some WILL BE HIDDEN..

in repairing the foam on my FLAPS (it disentegrates, especialy with
water and cleaners)  I used the FELT tack strip you by at the home store
for sealing windows/doors from drafts..

on the flappers there is a BLACK plastic 'retainer' use needle nosed
pliers to pop this off.
cut your FELT to length can/should drag on sides a little to seal.
and being mindful of how much your OG FOAM stuck out the flapper to
seal
position the felt on the flapper while with a sharpie mark the location
of the holes the 'retainer' snaps into.
cut "U" shaped notches in your flapper  (not the sealing edge) or punch
holes so the retainer will snap thru and hold the felt.

repeat,

I also used the 3/8 thin foam sealing welting you can buy near the felt
tack strip for around the base of the fan motor. and underneath fan to
body.

ODDS are your constant COLD draft would be your side vent ducts
loose/off  they have CONSTANT cold air pressure..

Why VW didn't put shut off flappers like they did with BAY Buses is
beyond me..

Dan
1980 ASI Riviera with TD conversion and now HEAT in the DASH>