I'm torn on the whole bug guard thing. Got a friend who swears they've prevented rock chips in their windshield. I'm skeptical - but I've got a lot more chips than he does!
Nonetheless, I'd think the Over Cab Fiberglass cap would totally mess with the wind flow and just makes me more skeptical that it could prevent a rock chip in the windshield.
But, I'll freely admit to never dragging a motorhome into a wind tunnel for testing!