A while back I posted pics of some salvaged grocery-cart plastic
cupholders that fit well on the lower cab heater vent shroud.

I now have 4 pairs available for $25/pair plus shipping. Add another
$5 of you want me to modify the backs to fit the vent shroud. Black
only.

I can only say they fit my 83 WBX manual Westfalia. No guarantees
they'll fit yours, or that the shroud won't slide off its fastener
tracks; just that they've worked well so far for me.