I got the '94 Toyota T-100, from mid-twenties to up to 39.9-mpg at 60-65-mph, strictly with aero. Four-banger, manual 5-speed, 2WD.
It's just a crude proof on concept.
Only you would know your limits on 'practicality.'
https://www.google.com/search?q=Stre...id:9AS-FbafeQ4