Most of your money is spent creating an enormous turbulent wake.
Any kind of boat-tail extension would pay you big dividends.
It could be built onto a receiver-hitch type cargo platform.
It could be an inflated structure attached to a swing-away spare-tire holder,inflated with any 12-VDC ventilation fan.
They've worked for me,they've worked for NASA.
It's probably the single best mod you could do.
