By the way I have tried some areodymatics on my Van.
And :
And:
So far: other than helping with cross winds and passing big rigs these are a big improvement over a stock van and I have driven 1000s of miles in vans...and the added rubber extras did not make the big improvement it was the original ground effect kit that came with this custom van...I love how much better it is on the road.
BUT so far if there was a improvement in MPG it was too small for me to note.
Rich