I stumbled upon an article talking about the short-lived Merkur (Ford Division) brand in the 80s.
Notice the 2 ailerons on that Merkur XR4Ti, clearly meant to reduce drag. It definitely is an interesting design that could be undertaken by us fellow ecomodders.
It would however obstruct the trunk if it were to be installed on a sedan. But that is manageable imo. The bi-plane wings concept is quite interesting to be honest.
For more info on the Merkur XR4Ti:
Merkur - Wikipedia, the free encyclopedia
Merkur XR4Ti - Wikipedia, the free encyclopedia
Cheers !