OP tries to slip one past us, but Youtube puts it on (at least my) front page:
TLDR; front undertray gives 45% benefit on the underside.
edit:
Further down the page:
Julian's grumpy video
2nd edit:
Make your own steel offcuts storage rack
I just use five-gallon buckets.
Car aero tricks and tips from the past
I had one of the examples, a 1961 Type II [panel van]. They came with a optional three piece bellypan between the axle lines:
(DDG, original page 404s)
But I believe these parts were used to stiffen the shell in the 23-window variants.
I would assert that the VW Beetle has a blown wake.
1500cfm, IIRC.