I think a lower airdam that extends/retracts based on the Vehicle Speed Sensor (VSS) output would be the bomb. You could make side skirts, and a front dam, and move those 3 pieces down close when there is little chance of ripping them off.
The only big problem is big road debris. One of those truck retreads could ruin your day
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2007 Dodge Ram 3500 SRW 4x4 with 6MT
2003 TDI Beetle
2002 TDI Beetle
currently parked - 1996 Dodge 2500 Cummins Turbodiesel
Custom cab, auto, 3.55 gears