Guys - Here's what I came up with; made from a 6 ft. length of rain-gutter cover I found at Home Depot and mounted to the underside of the cabover with aluminum angle, screws, and pop-rivets. I saw posts about this on the Overland site, with drawings, etc.; and then came up with my own solutions. The theory is that the defector substancially reduces wind noise (which it does) while the holes eliminate back pressure so dirt/dust does not work it's way up btw the cab and the camper. I just completed a 2.5 month, nearly 10,000 mile trip and it held up beautifully. The best part is there was nothing to mount of the cab roof and the cost was less than 20 bucks.
Cheers,
Tom