Ive noticed (from personal experience) the cars that allow less air under them tend to handle crosswinds better. I put a small "test" air dam on my Jeep and I noticed a difference in how it handled crosswinds. One of my friends put a front belly pan on his Mazda 6 and put several vortex generators near the front of it and noticed a difference in how it handled crosswinds. As far as boat-tails go, look at 3-Wheelers Insight.
http://ecomodder.com/forum/showthrea...ect-13533.html
as well as basjoos' aerocivic.